I frankly cannot imagine how difficult it must be - and I am so sorry that your parent's view of faith has resulted in you having to wrestle with a decision like this.
I'm sure you know - but I want to reiterate - that not all Christians believe that being LGBT is sinful. I would encourage you to have the "What the Bible Really Says" both handy and pretty well committed to memory - it won't instantly sway them - and they'll have counter arguments - but Mel has written a wonderful piece there and I've seen it help sway those who have only heard one interpretation.
I'd also commend the resources of PFLAG
- have some of their material handy - a great many of their members struggled to accept their children's sexuality, perhaps some of their stories will touch your parents.
Other's have responded to your questions better than I can - but I thought hearing from a "straight" Christian that you are okay might be helpful - so here I am.
I believe that God loves you - whether you, or your parents do - I can't change - but as a Christian - nothing - nothing - can separate you from the love of God. Be who you are - and thank you.