She is dating a Christian man and he has promised to become Muslim and marry her
Question

                i am dating a christian guy who promise to convert to islam bt i dnt if he can still change back to christian if he marry me finish,am afraid i love islam and i dnt want to go into another religion.,and another person is asking for my hand in marriage though he is a muslim bt he is married early last year and am thinking it too early for him to talk about second wife.i need your advice.
Praise be to Allah.
    First of all, allow us to remind 
    you of something that you neglected in your question, and it seems that you 
    are also neglecting it in your life, whilst you are continuing with this 
    behaviour and are far away from a good environment and a society that 
    reminds you of Allah, may He be glorified and exalted. This thing is the 
    fact that your dating your boyfriend is haram, and it is haram to be in 
    contact with a man in a love relationship outside of a legitimate marriage, 
    regardless of whether that man is a Muslim, a Christian or anything else. 
    Undoubtedly the sin and shame are greater if the man is a disbeliever, 
    because in the case of a Muslim there is the hope that you may get married 
    to him, but in the case of a disbeliever, that is nothing but wishes and the 
    deceit of the Shaytaan who makes these things seem good. 

    This kind of relationship will 
    either involve haram acts – Allah forbid – or it will be a path that leads 
    to them. The Shaytaan lies in wait for man and seeks to lead him astray, and 
    the human soul is inclined to follow whims and desires. No man is ever alone 
    with a woman but the Shaytaan is the third one present. Allah, may He be 
    glorified and exalted, says (interpretation of the meaning):

    “O you who believe! Follow not 
    the footsteps of Shaitan (Satan). And whosoever follows the footsteps of 
    Shaitan (Satan), then, verily he commands Al-Fahsha (i.e. to commit 
    indecency (illegal sexual intercourse, etc.)), and Al-Munkar (disbelief and 
    polytheism (i.e. to do evil and wicked deeds; to speak or to do what is 
    forbidden in Islam, etc.)). And had it not been for the Grace of Allah and 
    His Mercy on you, not one of you would ever have been pure from sins. But 
    Allah purifies (guides to Islam) whom He wills, and Allah is All-Hearer, 
    All-Knower”

    [an-Noor 24:21]. 

    You have asked for our opinion, 
    not on the basis of our personal opinions, but on the basis of our 
    understanding of what Allah loves and is pleased with, and what is taught by 
    the religion of Islam which we all follow, praise be to Allah, and which we 
    believe is the way to happiness in this world and the Hereafter. 

    We will give you sincere advice, 
    as you would expect, by Allah’s leave. We say to you: marrying a Christian 
    is definitely forbidden in our religion, and it is one of the most 
    reprehensible deed that a Muslim women could do. That is not marriage in any 
    way whatsoever; rather it is pure sin and a great evil, as Allah, may He be 
    glorified and exalted, says (interpretation of the meaning):

    “then if you ascertain that they 
    are true believers, send them not back to the disbelievers, they are not 
    lawful (wives) for the disbelievers nor are the disbelievers lawful 
    (husbands) for them”

    [al-Mumtahinah 60:10]. 

    The prohibition is not limited 
    to a case where you fear that he may make you enter his religion, rather 
    even if he promises you that he will become Muslim, it is not permissible to 
    rely on his promise; rather it is essential that he actually does enter 
    Islam out of a genuine wish to follow this religion and believing that it is 
    sound, and it is essential that he becomes a sincere Muslim – all of that 
    should come before doing the marriage contract. 

    Without that, we do not think 
    there is any confusion regarding your question; rather the matter is quite 
    clear. What you must do is repent from what has happened in the past of this 
    haraam relationship. Allah, may He be glorified and exalted, loves those who 
    repent and He loves those who purify themselves. If the Muslim is faced with 
    a choice between what is halaal and what is haraam, and he chooses what is 
    haraam, then he has no one to blame but himself, and he will see the 
    consequences of that in this world before the Hereafter. But if he chooses 
    what is halaal, and seeks reward for his patience and perseverance with 
    Allah, may He be glorified, Allah will reward him, by His leave. 

    Being guided and helped (to make 
    the right choice) is in the hand of Allah, may He be glorified. All that the 
    individual is required to do is take appropriate measures and weigh things 
    up by examining them rationally. It is essential to ask about the situation 
    of that Muslim who has proposed marriage to you, and what he has of 
    religious commitment and good characteristics that make him suitable to be 
    able to treat all his wives equitably. What you mentioned, about him only 
    having married his first wife recently, is not an impediment to marrying him 
    if he is suitable for marriage, and it is not an excuse. Moreover, you have 
    no excuse for giving precedence to the haraam relationship over him, or for 
    waiting for a long time with no guarantee. Plural marriage in Islam does not 
    require waiting for a specific length of time between one wife and another, 
    or a specific age; rather the matter depends on the wishes of each partner 
    and their compatibility. 

    Pray istikhaarah, asking Allah, 
    may He be exalted, for guidance as to whether you should agree to this 
    marriage, and ask Him to make it easy if it will lead to your happiness; 
    otherwise it is better that it be diverted from you by His protection. 

    As for the first relationship 
    with a non-Muslim, it is not permissible to pray istikhaarah concerning it, 
    because istikhaarah can only be done with regard to things that are 
    permissible, not things that are haraam. So you must immediately cut off all 
    ties with him and get rid of everything that may remind you of him or pull 
    you back into that relationship. 

    For more information, please see 
    fatwas no. 100148 and 99264 

    And Allah knows best.