Saying " you are 18, you can do what you want " is an idea achievable in principle if not in practice and I resent how some people instinctively seem to claim this is "nothing to do with religion".
May I invite everyone to look at statistics of homeless children in America who have been thrown out by their parents because they're gay - of course that almost always is for exclusively religiously motivated reasons - and consider changing their mind?
In any case arguing with facts will get you nowhere and I'd much rather people (presuming they are reasonable and sincere in the first place) didn't just automatically disregard or discredit a very real issue just because it doesn't necessarily effect them.
This issue doesn't effect me personally but I'm very aware of the fact that this is an all to common occurrence for people like you and me.
I don't have any solutions other than to suggest you " test the waters" and guage their likely response instead of writing them off straight away because parents should go on loving their children, they are still their own children.
And before anyone bites at me for thinking of all religious people as the same and me being just as fundamentalist as them let me add that of course there are good people who believe in god(s) but they are the ones who don't take their religion seriously. Don't agree? Change my mind! I'm not a fundamentalist because I know exactly what it would take to do it and would gladly do so in the face of such evidence.
I can't pray for you but I'd like to take the opportunity to wish you lots of luck in your situation and that you will get the outcome YOU have worked for and deserve.