<human>: Can you condense the text into a few key points?

I have recently gotten dumped, which led to the horrific demise of my year long relationship. My partner and I had decided to have a three way, at a party with one of our mutual friends. Everyone was sober, and my partner and I had thoroughly discussed the boundaries of threesomes prior. Everything had gone well and fine, until the next morning when we all were awake. We were with a big group of some of our closest friends that each of us had met through the same summer camp when we were kids. My now ex had done nothing but brag about the whole ordeal, and admittedly, I had a bit to, but was super touchy with the other girl. Over the course of the few days, my partner and I would argue. I felt as if I wasn't getting the after care that I really needed in the situation. I was very communicative and tried to talk about my concerns, but nothing was really done to accommodate how distant things had gotten. I ended up getting upset and lashing out, and over the week we would fight and makeup. One night after a dip in our relationship, he called me to end it. He said he couldn't keep forgiving me for being mean and blamed everything on me. This was two or three weeks ago, and I have found out that he is now dating the girl from the threesome. All of our mutual friends from the same party know, and everyone has all been hanging out without me. I feel really cheated, because I had trusted him enough to open our relationship. He had been talking to the girl since immediately after the threesome, and whenever we would fight before the breakup. It all sucks, but so many of our close friends have gotten involved and taken sides that it's incredibly overwhelming and I feel awful. Despite our friends wanting to remain impartial, many of them have said how awful both of them had acted, yet still continue to spend time with them, while I've dealt with this alone. The whole breakup has been blindsiding, and it hurts to see one of my friends take away the man who once swore to marry me. I would just like some advice on how to move forward, but still keep the friends we both had.
<bot>: Had threesome. Got dumped after a year long relationship. Ex begins dating the other girl shortly after. Friends are stuck in between.