He got to know her then he agreed with her that she would be his concubine!
Question

                About 6 months ago, through a (female) friend of mine I got to know a person who is travelling to complete his studies, and the way we got in touch with one another was via the internet. The way we spoke to one another was ordinary, like a brother and sister. He used to advise me about religious matters. About a month and a half ago, he asked to form a relationship with me and said that he would propose to me as soon as his studies finish, in two years’ time. But he surprised me one day by suggesting something I had never heard of before, to make it halaal for us to speak to one another and so that there would be nothing haraam in us speaking as two people who have a proper relationship with one another. He said that I should say to him, “I give my soul to you as a free Muslim woman, not any other man” and he would say, “I accept.” He told me that in this way I would become permissible to him and there would be nothing haraam in our talking to one another, rather we would become like a husband and wife. He described this to me as “mulk al-yameen” (what one's right hand possesses, i.e., a slave or concubine) and said that he had asked people who are specialized in this subject and they said it is permissible. But have my doubts about this matter and I tried to ask many people whether this is correct or not. Is there such as thing as mulk al-yameen nowadays or not? I am really confused and I hope that you can help.
Praise be to Allah.You should 
    note – may Allaah bless you – that our great religion has issued stern 
    warnings against forming relationships between the sexes outside the 
    framework of marriage. It firmly closes the door to the friendship programs 
    that have become widespread in newspapers and magazines and over the 
    internet; this is in order to prevent fitnah and to prevent love 
    relationships that usually lead people to immoral actions and transgression 
    of the sacred limits of Allaah, Allaah forbid, or leads them to marriage 
    which is likely to fail because it is based on suspicion and mistrust. 
You made a 
    mistake when you formed a friendship with a young man who is not related to 
    you. 
As for your 
    saying “I give my soul to you…” this is also wrong. Firstly, because it is 
    not permissible for a man to marry a woman without the permission of her 
    wali (guardian), whether she is a virgin or has been previously married. 
    This is the view of the majority of scholars, including al-Shaafa’i, Maalik 
    and Ahmad, because of the words of the Prophet  (peace and blessings of 
    Allaah be upon him): “There is no marriage without a wali”. Narrated by 
    al-Tirmidhi (1101), Abu Dawood (2085) and Ibn Maajah (1881); classed as 
    saheeh by al-Albaani in Saheeh al-Tirmidhi (1/318). And it was 
    narrated that ‘Aa’ishah (may Allaah be pleased with her) said: The Messenger 
    of Allaah  (peace and blessings of Allaah be upon him) said: “Any woman 
    who gets married without the permission of her wali, her marriage is 
    invalid, her marriage is invalid, her marriage is invalid.” Narrated by 
    al-Tirmidhi (1102), Abu Dawood (2083) and Ibn Maajah (1879); classed as 
    saheeh by al-Albaani in Irwa’ al-Ghaleel (1840). 
Secondly, it 
    is not permissible for a woman to give herself to a man, and she does not 
    become permissible to him thereby. This is something that applied only to 
    the Prophet  (peace and blessings of Allaah be upon him), and no one 
    among his ummah has the right to do that. Allaah says (interpretation of the 
    meaning): 
“and a 
    believing woman if she offers herself to the Prophet, and the Prophet wishes 
    to marry her  
    a privilege for you only, not for the (rest of) the believers”
    [al-Ahzaab 33:50]
 As for his 
    saying that this is “what one's right hand possesses” this is also wrong, 
    because a free Muslim woman cannot become a slave, rather the slave woman is 
    a woman from a kaafir nation that is at war with the Muslims, if the Muslims 
    capture her. 
Shaykh 
    al-Shanqeeti (may Allaah have mercy on him) said: The reason why a person 
    may be owned as a slave is kufr and waging war against Allaah and His 
    Messenger. If Allaah enables the Muslims who are fighting in jihad so that 
    the word of Allaah will be supreme to prevail over the kuffaar, then that 
    makes them their slaves.  
End quote 
    from Adwa’ al-Bayaan, 
    3/387 
Finally, we 
    would like to say that marriage which is based on anything other than a 
    sound shar’i foundation is bound to fail and will lead to regret. The young 
    man who forms such a long-term relationship with a non-mahram girl via chat 
    rooms and phones is in fact a young man who is lacking in religious 
    awareness, modesty and proper etiquette, and he is not to be trusted with 
    the honour of the Muslims. We advise you to repent to Allaah and turn back 
    to Him, and keep away from this young man. That will be safer for you, 
    before you regret it at a time when regret will be to no avail. You have a 
    lesson in the many stories which started with talking over the telephone and 
    ended in misery and regret. 
For more 
    information please see question no. 
    26067 
And Allaah knows 
    best.