well, I'd say not to be around him if possible, since he's so negative and seems to enjoy making you and others feel bad. Those kinds of people aren't worth being around. Negative energy spreads like wildfire, and sometimes a person is trying to send it out due to anger or depression and sometimes someone doesn't even mean to send it out.
If you can't cut him out of your life for some reason. Try shielding spells, to keep his energy from getting to you. And use cleansing after you're around him to get rid of any of the energy that may have gotten to you anyway.
Chances are, he's a troubled person who probably has some kind of emotional or mental issue. It may be a good idea to also do some work for him, Prayer and things of that nature, asking for this energy to leave him and him to wish to change his ways is a good way. Yeah, its difficult to do things for people who hurt you and are like that, but not only would you be helping him you'd be helping yourself and the people around him that are also effected by that energy.