I'm in the same exact same situation right now being estranged, maybe permanently, from a close friend due to a fight (hashed it out on here on this forum several weeks ago), and I second Auntie Venom's advice completely. You don't want your ex-friend to think that he's gotten the best of you and that you're no longer hanging out with this group anymore because of his presence, nor do you want to lose this core group of friends because they had nothing to do with the fight! You can still be in the same room and same event, but just stay a distance away from each other and if you are in the situation where you need to talk, make it short and civil. Most likely, your ex-friend and his GF won't want to make a scene either in front of the whole group, so they will do the same. If God forbid they don't, then just ignore whatever the two of them are doing or saying to you, and they will be the ones who look like idiots. This has worked out with my ex-friend so far, although I would never attend an event that is being held at her place because that would just be too awkward.