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