My relationship is being effected by others', this sucks!

[sweetjayguitar]

My two friends that were dating finally broke up. I comfort and support both of them during their rough times. But one of them Chris, on a group trip with friends as well as his former, had to go and open his big mouth and call her names that he shouldn’t have. The ex girlfriend, Mandy, has refused to talk to me about it and Chris hasn’t mentioned anything to me so officially I haven’t heard it out of the horse’s mouth but it was bad.
And well, Chris just called my cell and asked me if I was going out with the group tonight, I turned the invite down but accepted another one, to go to Hemmingway’s with him on Saturday night. When I told David my plans he got so upset with me and said that I was stabbing my friend in the back by going out with him. And I not hating Chris I thought would have nothing to do with out relationship anyways but he says it has everything to do with us. So David is pissed off at me because I’m playing both sides and being friends to them both. Is it me or does that seem somewhat stupid? And then he goes on to say that’s why he doesn’t have friends, but what do you call the people he hangs out with? Acquaintances, I hate when he refers to his friends as just acquaintances because each of them would gout out of their way to help us anytime and a lot of them already have.
I don’t know how to react.