I haven't tried it myself, but last year I was in a situation where 2 of my girlfriends and one of my boyfriends (all in the same friendgroup)'s relationships got pretty f…ed up. Girl A and Boy had been together all highschool, and Girl B was good friends with both of them.
But Boy and Girl B fell in love and flirted a lot, untill he finally broke up with Girl A, and the same night, kissed Girl B.
I found myself on both sides. I felt sorry for Girl A, but it wasn't like Girl B did me something, so I was still friends with her. In our group of girlfriends, some of them was mad at Girl B too, but most of us felt it couldn't be helped if they were in love, and as said, she didn't do anything to us. But most supported Girl A.
Even today Girl A and Girl B are still mad at eachother, but can be in the same room. But when Girl B leaves, Girl A talks bad about her. So annoying for the rest of us, we're so sick of hearing about it now. Get on with it!