All of these experiences have changed if not ended friendships. One study, examining the issue of envy in the triadic system of sibling, sibling-in-law and spouse, concluded that "The sibling-in-law relationship shared similarities with both spousal and sibling relationships " and that "Relational closeness and satisfaction for all relationships in the triad were correlated. I just can't see anything good coming out of this unless they end up happily ever after. Am I wrong to be mad about this? She is pissed at my best friend for sleeping with her sister and using her other close friend to get laid. My best friend also doesn't have a very good history with women.