I is back.
Really and truly, your parents need to understand that no matter what, your happiness and well-being should come first, as most parents in general should accept as the primary goal for their children. Regardless of what gender and such that their children lean towards, any sort of religious thoughts should be put away in this case; just because a two-thousand year old book written by Jews, put together by Pagan Romans, and translated horribly in some places by James I's scholars, says that it's wrong to be attracted to the same sex, doesn't mean that anyone should take those ideas and run with it.
In today's society, there are thousands of happy same-sex couples who are Christians. Sure, a church probably won't marry them together, but they still uphold most of the aspects and ideas of Christianity. Things change as time progresses, and unfortunately your parents can't force you to think what they want you to think. They can't control your mind, make up a personality they like for you, and try to make your life the way they want it to be.
However, as long as you are safe, happy, healthy, and of a sound, logical mind, your parents shouldn't have a real need to worry about your sexual orientation.
They should trust you to make choices that you want to make, not for their sake, but for yours. Only you can decide what's best for you, because your parents may share similar genes with you and live in the same house, but they are not one-hundred percent you.
Your parents should accept your choice, and give you the trust to go through with that choice. Trying to force you onto a road they know is 'right' won't help you at all - you're human, so you can make mistakes. If they choose not to accept it, well, they can keep their opinions to themselves. Whether they like it or not, its your decision in the end. They just have to understand your point of view-ish and be thoughtful enough to allow you to take that leap of faith-ish, and such.
Hopefully that helps!