Personally, I think the meaning of this song is about a girl cheating on her boyfriend and he found out.
So here's the long story. I think that there is a couple and the girl was cheating on the guy, but when he finds out he's heartbroken because he loves her so much. And he doesn't know how to confront her cheating ways. But when he does, she promises that he will be the only one, but he doesn't trust her anymore.
I love this song though, it's amazing.