Is the Quran the Word of Allah?
Question

May peace and blessings of Allah be upon you. I am writing in hope that you will be able to help me resolve my dilemma. I am a practicing Muslim woman ( 20 years old). I moved to XXX 5 years ago.   My parents were never practicing Muslims, but I've been taught about Islam from my grandmother.  

I've always been a believer in Allah. Until recently I did not know how to perform prayers; however I decided that there is nobody here to teach me so I had to do it myself.  
With the help of Allah, I learned how to perform them, also I started wearing hijab. 
The problem I am writing with is that I've been seeing this guy with whom I fell in love with. 
Unfortunately he is not a Muslim, but also he does not belong to any faith. He does believe in God. I've been trying to convince him to join Islam and become part of the only true religion, otherwise I cannot marry him. (We've been together for 3 years). What I cannot convince him is that Muhammad (pbuh) is the messenger of Allah. He keeps asking me questions like " How do you know that this is a word of God?
What if Muhammad just made it up as if it is a word from God. Please tell me how to convince him that Quran is a true word from none other but Allah and that Muhammad is the Messenger. Please help,
He keeps saying that if we were to get married he would not have a problem with me continuing to practice my religion. He is quite proud of me for starting to wear hijab in society where it is not common. (I might be one of the only people wearing hijab in this town, the belief in Allah gave me the strength to do it) I know that he would not have a problem with me practicing my faith, but I would still like him to be a Muslim. Even though he is a great person and does not do anything bad.  It really hurts when I think that we cannot be together.  Is it a major sin for me to get married to him? There are a lot of people who do it especially when there are no Muslims around where I live at all. There are a lot of Muslim women that do it. Would I be terribly punished if I were to marry him?
Praise be to Allah.Praise be to Allah Who has made good dear to you; we ask Him to increase you in guidance and faith, and to guide your parents to practice Islam and adhere to its rulings. 
Quran is the word of Allah
With regard to the Quran and the proof that it is the word of Allah, these are specious arguments which were put forward out of stubbornness and arrogance by the first disbelievers to whom the Prophet (peace and blessings of Allah be upon him) was sent. Allah refuted what they said in many ways, proving their words to be false and pointing out what was wrong with it. For example: 

In this Quran is a challenge from Allah to mankind and the jinn to produce anything like it, but they were unable to. Then He challenged them to produce only ten surahs like it, and they were unable to. Then He challenged them to produce something like the shortest surah in the Quran , and they could not do it, even though those who were being challenged were the most eloquent and well-spoken of mankind, and the Quran was revealed in their language. Yet despite that they stated that they were completely incapable of doing that. This challenge has remained down throughout history, but not one person has been able to produce anything like it. If this were the word of a human being, some people would have been able to produce something like it or close to it. There is a great deal of evidence for this challenge in the Quran, for example, the ayah (interpretation of the meaning): 

“Say: If mankind and the jinn were together to produce the like of this Quran, they could not produce the like thereof, even if they helped one another.” [al-Isra 17:88]
Allah says, challenging them to produce just ten surahs: 
“Or they say, He (Prophet Muhammad) forged it (the Quran). Say: Bring you then ten forged Surahs (chapters) like unto it, and call whomsoever you can, other than Allah (to your help), if you speak the truth!” [Hud 11:13 interpretation of the meaning]
Allah says, challenging them to produce just one surah: 
“And if you (Arab pagans, Jews, and Christians) are in doubt concerning that which We have sent down (i.e. the Quran) to Our slave (Muhammad), then produce a Surah (chapter) of the like thereof and call your witnesses (supporters and helpers) besides Allah, if you are truthful.” [al-Baqarah 2:23 interpretation of the meaning]

No matter how much knowledge and understanding mankind attains, they will still inevitably make mistakes, forget things or fall short. If the Quran were not the word of Allah, there would be some contradictions and shortcomings in it, as Allah says: 

“Had it been from other than Allah, they would surely have found therein many a contradiction.” [al-Nisa 4:82 interpretation of the meaning]
But it is free from any shortcoming, error or contradiction; indeed, all of it is wisdom, mercy and justice. Whoever thinks that there is any contradiction in it, that is because of his diseased thinking and mistaken understanding; if he refers to the scholars they will explain to him what is correct and clear up the confusion for him, as Allah says: 
“Verily, those who disbelieved in the Reminder (i.e. the Quran) when it came to them (shall receive the punishment). And verily, it is an honourable well fortified respected Book (because it is Allah’s Speech, and He has protected it from corruption). Falsehood cannot come to it from before it or behind it, (it is) sent down by the All Wise, Worthy of all praise (Allah)” [Fussilat 41:41-42 interpretation of the meaning]

Allah has guaranteed to preserve this Quran, and He says: 

“Verily, We, it is We Who have sent down the Dhikr (i.e. the Quran) and surely, We will guard it (from corruption)” [al-Hijr 15:9 interpretation of the meaning]
Every letter of it was transmitted by thousands from thousands down throughout history, and not one letter of it was altered. If any person tried to alter anything in it, or add something or take something away, then he would be exposed straight away, because Allah is the One Who has guaranteed to preserve the Quran, unlike the case with other divinely-revealed Books which Allah revealed to the people of a particular Prophet only, and not to all of mankind, so He did not guarantee to preserve them, rather He delegated their preservation to the followers of the prophets. But they did not preserve them, rather they introduced alterations and changes which distorted most of the meanings. The Quran, on the other hand, was revealed by Allah to all of mankind until the end of time, because the Message of Muhammad (peace and blessings of Allah be upon him) is the final message, so the Quran is preserved in men’s hearts and in written form, as is proven by the events of history. How many people have tried to change the verses of the Quran and deceive the Muslims, but they were quickly exposed and their falsehood was discovered, even by Muslim children. 
Another of the definitive signs that this Quran was not produced by the Messenger of Allah (peace and blessings of Allah be upon him) but that it came revealed by Allah to him is the following: 

The great miracles which the Quran contains of legislation, rulings, stories and beliefs, which could not be produced by any created being no matter how great his intelligence and level of understanding. No matter how hard people try to promulgate laws to regulate their lives, they can never succeed so long as they are far away from the teachings of the Quran; the further away they are, the greater their rate of failure. This is something that has been proven by the disbelievers themselves.  
Reports of matters of the unseen, both past and future, which no human being could speak of independently, no matter how great his knowledge, especially at that time which is regarded as primitive in terms of technology and modern tools. There are many things which had not been discovered yet, and which have only been discovered after lengthy and difficult exploration with the most modern equipment, but Allah told us about them in the Quran, and the Messenger of Allah (peace and blessings of Allah be upon him) mentioned them, fifteen centuries ago, such as the stages of embryonic development, the nature of the oceans, etc. These things have made some kafirs state that this could only have come from God, as in the case of the development of the embryo: 

Only 60 years ago, researchers confirmed that man does not come into existence all at once, but rather he passes through stages of development one after another. Only 60 years ago, science discovered this one Quranic fact. 
Shaykh al-Zindani said, we met an American professor, one of the greatest American scientists, whose name was Professor Marshall Johnson, and we told him that it says in the Quran that man is created in stages. When he heard this, he was sitting down, but he stood up and said, Stages? We said, That was in the seventh century CE! This Book came and said, man was created in stages. He said, That is impossible, impossible We told him, Why do you say that? This Book says (interpretation of the meaning):  
“He creates you in the wombs of your mothers, creation after creation in three veils of darkness.” [al-Zumar 39:6] 
What is the matter with you, that [you fear not Allah (His punishment), and] you hope not for reward (from Allah or you believe not in His Oneness).
“While He has created you in (different) stages.” [Nuh 71:14]
Then he sat back down on his chair and after a few moments he said, There are only three possibilities. The first is that Muhammad had a huge microscope through which he managed to study these things and he knew things that the people did not know, and he said these things. The second is that this happened by accident, it was a coincidence. The third is that he was a Messenger from God. We said, With regard to the first idea, that he had a microscope and other equipment, you know that a microscope needs lenses, and lenses need glass and technical expertise and other equipment. Some of this information can only be discovered with an electron microscope which needs electricity, and electricity needs knowledge which should have been acquired by an earlier generation. It is not possible for this knowledge to have been acquired all at once in a single generation; the previous generation would have had to strive hard in developing science and transmitting it to the next generation, and so on. But for this to be the work of one man, with no one coming before him or after him, either in his own land or the neighbouring lands for the Romans, Persians and Arabs were ignorant and had no such equipment for one man to have all these instruments and tools which he did not pass on to anyone else this is not possible. He said, Thats right, it would be very difficult. We said, And for it to have been an accident or coincidence, what would you think if we said that the Quran did not mention this fact only in one verse but in several verses, and that it did not refer to it in general terms but that it gave details of every stage, saying that in the first stage such and such happens, in the second stage such and such happens, in the third stage and so on. Could that be a coincidence? When we explained to him all the details of those stages, he said, It is wrong to say that this is an accident! This is well-founded knowledge. We said, Then how do you explain it? He said, There is no explanation except that this is revelation from above!
With regard to the many statements in the Quran concerning the sea, some of these facts were not discovered until very recently, and many of them are still unknown. For example, these facts were discovered after hundreds of marine stations had been set up, and after images had been taken by satellites. The one who said this was Professor Schroeder, one of the greatest oceanographers in West Germany. He used to say that if science advanced, religion would have to retreat. But when he heard the translation of the verses of the Quran, he was stunned and said, These could not be the words of a human being.   And Professor Dorjaro, a professor of oceanography, told us of the latest developments on science, when he heard the verse: 
“Or (the state of a disbeliever) is like the darkness in a vast deep sea, overwhelmed with waves topped by waves, topped by dark clouds, (layers of) darkness upon darkness: if a man stretches out his hand, he can hardly see it! And he for whom Allah has not appointed light, for him there is no light.” [al-Nur 24:40 interpretation of the meaning]
He said:
“In the past, man could not dive to a depth of more than twenty meters because he had no special equipment. But now we can dive to the bottom of the ocean, using modern equipment, and we find intense darkness at a depth of two hundred meters. The ayah says a vast deep sea . The discoveries in the depths of the sea give us an understanding of the verse, (layers of) darkness upon darkness. It is known that there are seven colours in the spectrum, including red, yellow, blue, green, orange, etc. When we dive down into the depths of the ocean, these colours disappear one after another, and the disappearance of each colour results in more darkness. Red disappears first, then orange, then yellow and the last colour to disappear is blue, at a depth of two hundred meters. Each colour that disappears adds to the darkness until it reaches total darkness.  With regard to the phrase waves topped by waves, it has been proven scientifically that there is a separation between the upper and lower parts of the ocean, and that this separation is filled with waves, as if there are waves on the edge of the dark, lower portion of the sea, which we do not see, and there are waves on the shores of the sea, which we do see. So it is as if there are waves above waves. This is a confirmed scientific fact, hence Professor Dorjaro said concerning these Quranic verses, that this cannot be human knowledge.” (Al-Adillah al-Maddiyyah ‘ala Wujud-Allah by Muhammad Mutwalli al-Sha’rawi) 
And there are very many such examples 

In the Quran there are some verses which rebuke the Prophet (peace and blessings of Allah be upon him) and mention some things to which Allah drew his attention. Some of them may have been embarrassing for the Prophet (peace and blessings of Allah be upon him). But if this Quran had come from the Messenger of Allah, there would have been no need for this; if he were to conceal any part of the Quran, he would have concealed some of these verses which contained rebukes or drew his attention to certain matters which he should not have done, such as the verse in which Allah says to His Prophet (peace and blessings of Allah be upon him): 

“But you did hide in yourself (i.e. what Allah has already made known to you that He will give her to you in marriage) that which Allah will make manifest, you did fear the people (i.e., their saying that Muhammad married the divorced wife of his manumitted slave) whereas Allah had a better right that you should fear Him.” [al-Ahzab 33:37 interpretation of the meaning]
After this, can there be any doubt left in the mind of any intelligent person that this Quran is the word of Allah, and that the Messenger (peace and blessings of Allah be upon him) conveyed that which was revealed to him in full? 
Moreover, we tell this person, try it for yourself, read a sound translation of the Quran and use your mind to ponder these rules and regulations. There is no doubt that any intelligent person who has the power of discernment will see a great difference between these words (of Allah) and the words of any person on the face of the earth. 
Man-woman relationship in Islam
With regard to your relationship with this young man, this noble religion forbids women to mix with men for a great and wise reason. So you have to stop meeting him and break off your relationship with him until he becomes Muslim, in which case you can marry him in a proper Islamic marriage. In the answer to Question no. 1200 you will find an explanation of the rulings on a Muslim woman mixing with non-mahram men. 
With regard to your love for him, this is a test from Allah: will you put your love of Allah before your love for one of His creation, or will you put your love for this person before the love of your Almighty Lord Who has forbidden such things. Note that whoever gives up something for the sake of Allah, Allah will compensate him with something better than that, the first of which is that you will find, in sha Allah, that Allah will compensate you with comfort and tranquility in loving Him and striving to draw closer to Allah by means of that which He loves; so your love for your Lord and your attachment to Him will increase, and  your attachment to all of His creation will become weaker. In the answer to Question no. 10254 you will find some solutions to this problem. 
Can Muslim women marry non-Muslim men?
With regard to the ruling on a Muslim woman marrying a non-Muslim man , this is haram according to scholarly consensus, indeed it is one of the major immoral actions which Allah has forbidden in the Quran. In the answers to Questions no. 8396 and 1825 you will find a detailed response to this question. 
We advise you to be patient and to put up with difficulties, and to keep far away from everything that may cause you to do things that would anger your Lord. Note that Allah has made this world a place of trial and testing for His believing slaves; whoever is patient and refrains from following his desries, seeking the pleasure of Allah, Allah will compensate him with Paradise where He will bestow upon him all kinds of delight which cannot be compared with the fleeting worldly pleasures that he sacrificed. This is in addition to the happiness and tranquility that he will find in his heart when he obeys his Lord. 
Perhaps if he sees how you adhere to your religion and avoid meeting him and sitting with him despite your love for him, he will come to realize the greatness of this religion which makes its followers prepared to sacrifice all that they love in order to please their Lord, and that they hope for a great reward from their Lord for their patience in obeying Him and keeping away from that which He has forbidden and perhaps that will be the cause of his becoming Muslim. 
We ask Allah to guide him to Islam, and to make goodness easy for you, and to keep all evil away from you, Ameen.
And Allah knows best.