I suppose this counts. Girl I dated in high school and college broke up with me. Still hung out with her and things were cool. She and my best friend started acting suspicious after a few months. They started hanging out without me then lying about it and such. I tried to get the truth, but for months they wouldn't budge. Eventually it came out in one of the worst ways I can possibly imagine (whole different story there). I was pissed not that they were dating, but that they lied to me for months when I otherwise wouldn't have given a fuck.

Didn't speak to either of them for about six months. Eventually started hanging out again. Everything was cool. They dated for a few years during which we were all pretty tightly knit even if things were occasionally a bit awkward. Then my best friend broke up with her.

She went berzerk. Friend tried to be civil, kept hanging out, remained friendly, but every time she dran she threw a tantrum. She got paranoid that we didn't want to hang out with her, which I understood from my own experience, but in my case I was proven correct to some extent.

Things quieted down after a few months, the normal friendship dynamic resumed. Then out of the blue my friend gto back together with her. Now, they're off on some kind of vacation I'd normally have been invited on and the awkwardness of the situation is that I really am being left out so that they can work through their own issues by fucking. It seems that in the end I'll get the short end of this relationship stew one way or the other. Either the dynamic stays awkward couple and a third wheel, or everyone involved has to deal with the wave of breakup dramasplosions. And I am deathly allergic to drama.