Is it permissible to continue an emotional relationship with a Christian girl with the intention of inviting her to Islam and marrying her later, knowing that the relationship is free from overt prohibitions, has increased the questioner's religious commitment, and that the girl needs an explanation of the details of the Islamic religion?

Establishing a relationship between a man and a Christian woman before marriage is Haram (definition) (forbidden) in Sharia (definition), and it is not justified by the intention of marriage or her conversion to Islam. A Muslim must strengthen his faith and engage in Da'wah (inviting to Islam) through legitimate means, and avoid situations of temptation such as being alone with a non-mahram (definition) woman and looking at what is forbidden. This is in accordance with the Almighty's saying: "Tell the believing men to reduce [some] of their vision and guard their private parts. That is purer for them," and the Hadith (definition): "No man is alone with a woman but her Mahram is with her." If the communication is through writing or other means of communication for the purpose of inviting her to Islam, with security from temptation, then there is no harm in it. It is permissible to propose to her if she is chaste, and after marriage, he should invite her to Islam. If the marriage does not take place, the relationship must be severed and one must repent to Allah.