I don't like answering these kinds of questions. Because I'm not out to hurt anyone. But if this is the case, it could mean a few different things. None good come to mind though. (I really hope these are not the issues!)

When I use to act this way it was either because I got bored of her. Like it wasn't enough to keep me into the relation.

Maybe interested in another girl.

But let both hope you're just over thinking this whole thing and reading into hints that aren't really there. Because no one deserves a broken heart.

I hear about these problems often this could be that there's a third person involved or he is in change of mind of something that happened between the two of you im a psychic reader so this is alot of what im prone to fixing I would advise that you confront him about it