What's the proper response to the dissolution of a friendship within a social group?

I loved your your May 6th, 2012 discussion of "unforgivable acts," and I have a follow-up question. Now -- after cutting my losses with a best friend, after years of giving second chances, talking with him repeatedly, and determining that there's no more basis for a friendship -- how do I judge mutual friends of ours? Some of them think that my actions weren't justified. Some resent me for breaking up a group of friends. Many want me to either make up with this person or tolerate him at gatherings. Is this reaction by these mutual friends fair? How should I respond to them?