I had sex with a guy who had a girlfriend

A little while ago I texted one of my old friends because I wanted to reconnect. We ended up seeing each other at the mall and we were flirting with each other and then we had sex. He never told me that he had a girlfriend, I swear I didn’t now. If I had known I wouldn’t of done it. I am so heartbroken because the situation is so confusing and complex. My heart is hurting. I feel so horrible, I didn’t mean anything by it. I thought I was the only person that was going to end up hurt. I don’t even know what happened between the two of them. But I am “that bitch“. I’m going to be that person that her boyfriend had sex with because she wouldn’t have sex with him. I feel so stupid and so horrible. He used me but I feel like it’s all my fault.

I know you guys are probably not going to be very nice in the comments. But I’m already broken so my situation can’t really get any worse. Thank you for reading this, and please understand,I didn’t want it to happen like this.