This means nothing without a diagnosis at least. If he seriously considers his behavior a problem, he should seek professional help, no?
What you are describing could just as easily be moodiness and/or poor impulse control.
It was good of him to take the initiative to apologize.
But.
Are you willing to give him a continuing pass on taking his emotions/frustrations out on you? There's a difference between venting *to* someone and venting *at* them. Has this been a long-term pattern?
"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." -- Frank Herbert