I have taken classes on on mental disorders and worked with those with developmental disabilities for four years. His mood swings are too frequent and his high aren't high enough and lows aren't low enough to be a serious case of bipolar. But you may be right, it maybe a psychological disorder. Maybe it is a mild case of bipolar or something similar. He is taking an Abnormal Psychology class soon, maybe he will discover his own problem during the course. I think he gets part of it from his mom. She is a control freak and gets stressed out sometimes but he is worse than she is.
The first time I ever saw interaction with him and his daughter was when we took her to play miniature golf and was yelling at her because she wouldn't hold the golf club correctly no matter how many times he showed her. Finally he told her she couldn't play anymore. I got onto him about it and reminded him that it is a stupid game and he needs to chill out. After that he let her play her way and she finally started having fun. I wish I could be around more to defend her but I live 200 miles away.
As for the drugs it is highly unlikely. Just a few weeks ago he went to a persons house with a friend of his but left because they broke out marijuana. He doesn't want to be around or associated with anything of that sort. If he wouldn't be around marijuana I doubt he would be involved in anything worse.
I do appreciate your advice but mostly I just need to vent. We are going to do a trial "live together" from August until December and I think it is a good opportunity to either work on his issues or to discover that we just aren't compatable and need to stop wasting our time.