I introduced him (best friends since childhood) to a female friend of mine I had met seperately and they never really knew each other that well (went to different high schools and such). They eventually, after dating for about a year and a half became engaged. We had alotta fun before they got engaged, I never felt like the third weel when it was just the three of us. After they got engaged, he totally starts flippping out about me being friends with her, first in a passive-aggresive way, later verbal rage and threats of violence. Extremely paranoid about her cheating with me (there was never any attraction between me and her, not that it mattered, wouldnt have done such a thing in any case). It escalated to the point I said goodbye to both of them. They didnt get married, apparently she cheated on him but I've no idea if that's actually true. Still hurts thinking about it after almost 5 years, mostly because I still dont understand how this guy I knew for almost 20 years became a psychopath out of the blue.