Cheating that on a massive, destructive degree

I have a sis I care about so much. She just broke up with her 8 year relationship with her bf because he cheated. It was bearable if the 3rd party was a bitch but NO. It was a DUDE. My sis has been crying for weeks now and can't function properly. I have nothing against the LGBT community but I wanna kill that guy so much. I mean, it's not just that trust was broken but her confidence as a woman dropped from 100 to 0. What's worse is that the 3rd party had a lover too (a dude too for christ's sake) who fell for my sis' ex AS WELL. Just what kind of fuckery is this. Is this some kind of bl threesome or what. Messed up bullshit. My sis is so devastated and I am extremely disappointed cuz that asshole met our parents and had the prospect for marriage. I want to go up to that son of a bitches' place and throw him those punches he deserves.