Threesome gone wrong

So my boyfriend and I have been dating for a year and a half. We recently took a vacation and I wanted to try something different, so I suggested a threesome. It was my idea completely he had never brought it up. Anyways, we find the right woman and go to the hotel. The whole time this “threesome” happened it was mostly the two of them having sex. The girl seemed to be mostly interested in my boyfriend. So I sat there watching my boyfriend have sex with another woman and I couldn’t even join in. I felt so left out and unwanted. What I’m wondering is did we cross a line we can’t come back from? I feel like he cheated in a way but I also feel like I can’t be mad because I wanted the threesome and I chose the girl. What do I do? Please no negative comments, we like to be adventurous.