I slept with my boyfriend’s best friend for revenge

This happened a long time ago when I was 17/18 I’m 32F now. I’m not a great with details so bear with me I’m going to try my best. So when I was 17 I met this guy through my brothers now ex wife. He came over often and we would play video games together and just hang out and smoke. A couple months into our relationship we left and went to stay with my stepmom and his best friend came with us. At this point I had quit school and had no job neither did he. Eventually he found a factory job and as did I and we worked there for some time. Well eventually his best friend told me that he had slept with my stepmom but not only did he sleep with my stepmom he had also slept with my sister in law. Well when I found out I just sat quiet about it. A couple weeks later he went on a road trip with his dad so as soon as he left I slept with best friend and I called him right after and told him and also told him I knew he had slept with my SIL and stepmom. After the phone call I went home and I never talked to him again. I never told anybody this but it feels great to get it out. Thank you for listening.