Hey, I was in this position - my boyfriend was religious, didn't believe in sex before marriage, and I wasn't religious and did believe!
We tried waiting without him talking through his reasons with me, and it was hard, and we ended up giving in. The difference was that then I became a Christian. My advice to you is to get her to explain her reasons to you, because it will be easier to understand. Also, why don't you have a look at some info about christianity and the like because its really not a religion about denying yourself
its about love and peace and just making your life a million times better.
It is possible to wait, I know people who don't have sex before marriage on moral grounds. Like Handy said, you can still ejaculate frequently, it just means a wait for marriage for the big old event.
Edit: and also, I've found that our relationship has so much more foundation on friendship and fun and knowing each other than the physical side of things. the physical side will be great when we get married, and good fun, but it is NOT the most important part. I know a couple who are very close but relied very much on sex to keep them that close, on the natural intimacy that sex creates. But relying on this can lead you to think that as a couple you are closer than you actually are. At the end of the day, would they be there for you if you weren't having sex? That is a question that some couples don't want to have to ask. If you can ask that and say "yes", you know you're on to a good thing.