<human>: Can you give me the gist of the text in a nutshell?

Earlier this year I was dating a girl. Things were going great, we two really liked each other and loved spending time with each other. We had been dating for about two months when I found out that she was still sleeping with her FWB. 

There had been a at least one time where she told me she was hanging out with her room mates but was actually over at her FWB. I was really hurt to find this out. I wanted to give her benefit of doubt that as we had never discussed exclusivity so it was okay for her to do whatever she wanted. But I was not okay with the fact that the she lied to me. That and the intrusive thoughts got to me and I ended up breaking up with her.

I told her the reason that I was breaking up with her was that because she preferred to go have sex with her FWB rather than spend time with me. The break up happened about 4 months ago and I have been NC with her ever since. She has tried to get in touch with me a few times but I was still hurting and didn't want to talk to her. 

Fast forward to this week, she sends me a text apologizing for her actions and saying that she wished "that event" had never happened. From what I know about her, I feel like she is regretting the decision to sleep with her FWB and wants me back now. 

I really liked and still have feelings for her. But those intrusive thoughts still haven't died down. I don't know whether I should take her back because her action can be justifiable as it was a gray area while the relationship wasn't clearly defined. Or stay strong and not take her back because she also knew she was crossing the line when she lied to me about whom she was hanging out with.
<bot>: SO of two months was still sleeping with her FWB. I broke up 4 months ago. She apologized for her actions and seems to want me back. Do I take her back?