There are a few things you can do to get your best friend/lover to stay in love with you:
1) Switch religions or congregations. Not all religions are close-minded and bigoted. There are many out there that are open to the gay lifestyle. Look online to find the closest one in your area and bring your girl there with you.
2) Sexual favors can go a long way towards taking ones mind away from feeling guilty. Perhaps you need to give a little more in that department.
3) Start your own religion and have your girlfriend join. Problem solved.
Try respecting her choices and brace yourself for a breakup. Next time you get with someone, make sure you are both on the same page on topics like this.
Are you the butch or the femme? In my experience, the femmes are the ones that go running back to the straight life (often over religion), the good news is this....if you are the butch, its easier to see that you are gay and you will be hit on more than a femme will. lol
seriously though...this will not end well for you babe, and the best thing you could do is to brace yourself, let your woman know you respect her decisions and you are going to let her make those choices.
Good luck babe!
I find it funny that this response is next to an online Christian University ad.
If you're positive you are gay, then you and your girlfriend will probably have to change churches. Don't expect the church to change for you. The more conservative they are, the more they will dig in their heels. I hear the Unitarian Church is a good place to go; just tell family and friends that you and your "friend" are going to church elsewhere, they don't need to know the details. You and your girlfriend may still drift apart, but rumors get started at church too, and there's a lot more finger-pointing than other places.
Regardless of where I stand on an issue, I really don't think judging others is my job. It's God's.