I'd love to say I think a romantic relationship between a Christian and someone else could work, but honestly, I don't think that's possible. There is too much difference. If you are living your life for God, trying to follow a Biblical code of morality and making choices based on your faith and God's guidance, and this guy doesn't even believe that stuff exists, what have you got in common? If you think about where your relationship is headed, would you want to be married to someone who did not value your faith and was unwilling to genuinely join into a covenant with you and God? Because that is what marriage is. Personally, I think friendship is always possible unless the person actively tries to dissuade you from believing, but a romantic relationship is something more. Even if he does become interested in learning more about Christ, it's not a good situation to be in. My advice is stay friends, continue to share your beliefs with him and encourage him to find mentoring within the church, preferably by an older man.