salam, if she is not muslim and doesnt believe in Allah then u shouldnt marry her. i understand u used to date and u stopped when u became a muslim. in islam, it is haram to mix with girls and dat. fair enough u were talking about the deen but sometimes u have to sacrifice some things for the sake of Allah, and Allah will reward u for it. but if u keep mixing with dis girl, u will be tempted into haram. its ur choice but i think this girl is just part of ur old life, ur haram christian life. islam is ur future and this girl will might just get in da way and u might end having feeelings for her again, start dating her, and go back to ur old ways. some things u just have to let go, even if it seems impossible and Allah will reward u for ur efforts.