Mood swing, aggressiveness, high sexual desire are generally symptoms of increased heat in the body and its influence to his mind. In ayurveda this type of personality are called as pitta type. They will be very charming, commanding, leadership etc when balanced, but when heat aggregate they express such symptoms.. It's nothing to worry.
Next Steps
Encourage him to agree for a counseling session to open up, what's in his mind and agree for few lifestyle changes. It's should help.