Some people do meet their life partner that young. My mum met my dad when she was 16, and they've been together ever since (close on half a century!) But as PDM said, it's rare.
Think how much you've changed since you were, say, 12. It's only four years, but you've undoubtedly grown up and altered a hell of a lot in that time. You'll go through a lot more change by the time you're, say, 21. That's why most teenage relationships don't survive, because you're both changing and growing as people, and the things you thought you wanted at 15 or 16 may not be what you want at 20. Does that make sense?
Anyway, I know it's easy for us oldies to sit here pontificating about it.
I know you're suffering, dude, but it'll pass, and when it does you'll be wiser for the experience. Trust me!
