What happens when someone comes off this type of medication?

The person I was kindof seeing who is also a friend (we've recently fell out), has changed completely from being sensitive and caring and had difficulties maitaining an errection in bed to mean and thoughtless who has no problems in the bedroom now. He is also a very angry behaved person just now and keeps losing it verbally and violently. I know he was on some sort of medication I think for either depression or Bi-Polar(manic depression) or even some sort of anti-psychotic stuff. He always drank a lot but now is heading for the gutter and drinking horrendous amounts quickly. I was happy to stick by him as a friend but he as turned on me also. Does it sound like a change in medication or that he is off medication? Help, he means a lot.