I am not a Christian, but my fiance thinks I am one, what should I do?

I met my fiance in college and we started dating. My parents are evangelical Christians and I am not meaning although I believe in a higher power I don't believe in the Christian theology. He attended their church (I was at home for the summer). My parents rule is when I am under their roof I attend church and participate in all the church activities. So, we started dating and we attended chuch together, did all the church activities together, etc. When fall came I moved back to college three states away. Although I don't attend church, I do a lot of volunteer work, so we would talk long distance about our activities and he would talk about church. He thought I didn't attend while I was away at college because I could not find a church that was theologically sound and whenver I came home I would be in church. He never asked me outright, so I didn't outright lie. And I really liked him and it was just casual (meaning we saw other people). When I graduated and moved home last year all of a sudden it seemed to get really serious. I saw him at church the first Sunday I was back and it just hit me like, "that's the guy I am going to marry.' We started going places other than church and church activities and we were always talking about ourselves, not religion. In the meantime, I got a job and started saving up. Last week two things happened, I moved out of my parents house into my own place and he asked me to marry him in two years when he comes back from his missionary work in Nepal (he will be gone for two years, no visits). I am not sure what to do. I promised myself as soon as I was out on my own I would stop the farce of attending services of a religion I don't believe in. At the same time, I am SO in love with this guy and I know he is with me. But he doesn't know the truth about this one aspect of me. I asked him for some time to think about it, but his plane leaves on Friday and he wants an answer. I don't know if I should tell him. Or, another part of me loves him and has no problem attending a church he believes in so much, and attending church activities and even raising our kids Christian. I have no problem with Christians, I just don't believe in it. So, is it permissible to marry him and participate in a Christian lifestyle with him like I did with my parents, just because I love him and I think he would feel morally bound to either "save" me or leave me and it would break both our hearts...