So my best friend had a boyfriend at the end of the previous school year. And then we broke for summer break. Before break, they defined their relationship as polyamorous (having several sexual partners at once) her bf was the one that proposed the idea and it was a very new concept to her but she went along with it anyway. At the beginning of summer I was hanging out with her bf (because we're pretty close friends too) and another friend one night. We played truth or dare and one thing led to another. We ended up all 3 in the bed together, naked and horny. The two of them had sex, but I just partook in the foreplay. I had my concerns before anything started and asked if this was a good idea and he said he do whatever the fuck he wanted because he was in a ploy relationship. The next day her bf calls her and tells her what happens because he wanted an honest open relationship. My best friend told me when I contacted her a few days later, she was pissed a little bit then drew the boundary of no hooking up with friends. That boundary was not made beforehand. Now a few months later, she's just now getting angry about the situation because the two of them broke up recently. She counts it as cheating. Did he cheat on her with me?