Well, the pot wouldn't necessarily explain his behavior. He just sounds like someone who doesn't know what he wants, doesn't want to admit he has a problem with alcohol and probably drugs, and wants to blame everyone else around him for everything that's wrong in his life.
You may never figure out what's wrong with him or the root cause of his problems, but you will definitely drive yourself crazy trying to figure it out. Try to stop focusing on him and keep your thoughts on your little one.
Hugs,
JG