Hi, welcome to SR. I was married to an addict for 25 years. If I were betting, from my own experience, I'd say he's happy when he's high and sad/depressed when he is crashing. But you really can't know for sure.
The key to the whole recovery process for YOU is to learn to focus not on trying to figure out what he is thinking/feeling/doing, but to focus on your own feelings and needs. It is difficult at first to do this when for so long he has been consuming your mind. But it can be done.
Are you attending any '-anon' meetings (support groups for people who are affected by a loved one's addiction)? If not, that is a great place to start because you will find folks there who really know and understand what you are going through. Keep coming here, too. This place was instrumental in my recovery.
((((HUGS))))