I have done this to a couple of people for similar reasons. Over time, they really began to dislike some of my other friends, and eventually started going on vendettas and nasty, aggressive smear campaigns against them in places where they couldn't defend themselves. When I tried to defend the victims, I became their next victim. I dropped them like a hot potato after that, and shut them out of my life forever. Should have done so long before I did in all of the instances though. I haven't looked back since.
I'm learning not to get involved with people who play these nasty games in the first place, and am wary of red flags and warning signs.