If you're having these feelings, the possibility of marriage is always there. Everyone thinks they can overlook their differences in the love and passion of dating. I'm sure the two of you can look through that difference. When a child comes into the picture, a whole new set of problems emerge. Remember, the other person has been trained his whole life that if his child doesn't follow in his faith, that child will burn in hell for eternity. Whether or not your believe that, he does, and i guarantee this issue will come up if you have a child.
Please, make sure that the two of you are clear on this issue before your proceed. From someone who's been there, done that, and got the scars.
All Christians think that God brought them and their significant other together. Christians also have a very high divorce rate. Be very alert to magical thinking, especially on his part. I'm a psychologist, and I have the sad job of trying to help people get their lives back together after experiences like this.
I hope I haven't come off as negative. I've just seen the pain that can result when people have differences like this. This is a conversation you need to have with him. It's better to decide now if you can or can't live with this difference the rest of your life, than after there's a child in the equation.