You might find he frequently starts fights with you.This might be his way of getting you to gradually distance yourself from him.He might call you less often; when you try to reach him, he may not return your calls or texts as promptly as before.
When you are together, he doesn't pay attention to you like he used to.
Everyone forgets details sometimes, but if your boyfriend doesn't ask about a serious problem you shared with him, it's a sign he no longer cares.
He stops making plans for your future together as a couple.
For example, if there's a long weekend coming up, he talks about what he wants to do without checking to see what you'd like to do.
His interest in movies and music might suddenly be different.