A Year of Bad Decisions

I know I may sound stupid and this question may have a simple obvious answer but...I guess I just need to hear from someone else. I'll try to make the story short but the whole story none the less. In 2019 I was having an extremely hard time. I just quit my job because of an incident that happened between me and a fellow employee. It's not that no one believed me but it turns out the cameras were not working when the incident took place. Higher ups didn't want to pursue it so they just closed the file after giving him a write up and classes. I couldn't really cope with it all and I was barely showing up to work because they couldn't justify changing our shifts even during the investigation when he realized that I had reported him. Plus I wasn't confident I could keep doing a good job constantly looking over my shoulder. Things didn't really go well after that I retreated back into myself. I barely went out. I just kept blaming myself and regretting even coming forward. I just wanted to get out of my head. When I was finally managed to get myself together and get some kind of employment I met John. It was friendly at first we had an alarming amount of things in common and he wasn't scared away by my sadness. Eventually we started a relationship and it distracted me from everything in my head. What I'm about to say is really stupid but to add context I've always been a good girl following the rules not dating till college even so I didn't have much in the way of dating or relationships. I wanted to shed that persona that always seemed to do more harm to me then good. So I decided to take a walk on the wild side and do things I wouldn't normally do with him including agreeing to have a threesome with another girl. I was nervous at first but he supplied me with alcohol and other substances. While I was seriously out of sorts he told me that the woman we were about to meet was actually his wife who he has an open relationship with. We all got together a multiple times but most of the times he would just sleep with me. Eventually, his wife told me that she was pregnant again and began to leave whenever John and I would meet. Ultimately, they both began to fight about her pregnancy, his attention to her, and constantly seeing me. I kept trying to break it off but I was addicted to his distracting me and I couldn't stop seeing him. Later last year he told me that his wife who is pregnant had tested positive for an std and I needed to get tested. It was my first std and honestly I didn't know how to feel about it other than mortified. I decided after getting tested that I needed a break from them to get perspective. It just so happened around that time his wife lost it and sent me a message from his social account saying that not only did she tell him she no longer wanted an open relationship but after reading our messages to each other that he actually spent the night with me when she was sick in the hospital and she was filling for divorce. I decided to take this as an out and delete my account and cease all contact with him. Until February I'd spent several days wondering if he and she was okay and beating myself up for helping cause this. So I decided to check another social media account that we used and saw that he messaged me three times begging me to call or text him. Against my better judgment I did and we met and slept together. It didn't take me long to realize I was exhibiting signs of an std. I know this probably seems cut and dry but I just need to the extra push. I'm going to stop seeing him I just need help with what to say to him and do.