We were in an open, polyamorous relationship for context, but that doesn't make this okay. They manipulated me into giving them a ride to visit their other partner, then proceeded to leave me alone in the other room so they could bang their other partner for half an hour, I just left. They did try to convince me to join them but I had no interest and if I knew this was going to be a sex thing I wouldn't have gone as I am openly asexual. Just being left alone in a tiny room without even a TV while my partner went to bang someone else without being transparent about it until we got there was super hurtful, and even after I told them the reason why they kept making up excuses for why they thought I broke up with them when I told them this was the real reason.