Honestly, I don't think this is a good idea. I'm not doubting that you are in love---I'm not one of those people that says that you can't feel such strong emotions at such a young age. I'm 26, and I distinctly remember being 16. I remember feeling like an adult at that age. And you are, to some extent. But let me tell you, every year that I get older, I look back and think: I can't believe how I thought things were when I was younger...You do get wiser with age and, at 16, you should be enjoying being 16. Why thrust yourself into a world of rent payments, bills, jobs and possibly kids while you still have so much time left to be completely selfish?
If this is about sex, your parents seem supportive of you entering into marriage so perhaps they'd understand if instead, you and your boyfriend carried on a responsible sexual relationship. In the mean time, he may be the guy of your dreams now but 5 years from now, maybe not. Give it some time.
Also, having serious doubts the day before is a very good indication that you just aren't ready to get married.