Unsure what my next move may be in this relationship/friendship?

Bon matin to all of you viewing this thread,

This woman and I have been together for two years and ten months, another year and a month seperated but still in contact with each other. As I was away in a facility for quite some time, around six-eight months into my stay, she asked for a break, and I accepted and respected her decision. During my absence, she had sexual relations with three other guys before the ‘break’, and had a relationship (which lasted about two months) with one of the guys after our ‘break’.. During her relationship with him, the guy did not exactly treat her respectfully. From what she has told me, he has not beaten her, but simply became sort of a controlling factor in her life. Shortly after my release from the facility, the guy goes on to explain to her that ever since I have gotten back, she’s changed, and that she is being ridiculous (when in reality, he was more upset and angry over her wanting to be with me, more than him), he proceeded to threaten me to which she responded by telling him they were done. I’m not exactly sure why she did not put a stop to the relationship before. And not too long after, the guy apologized to her for the occurrence, and since it was she who was in contact with him, not me. Telling her that he would never hurt her or anyone she loved, then as she remained persistent, he turned back to the disrespectful persona and insulted her, even told her he wanted nothing to do with her. Well, you guessed it, he attempted on multiple occasions to call her and text her and when she decided to respond, he apparently became “sincere” in his words and intentions. She expressed to me that the reason she has not tried to tell him to back off is because she doesn’t want to hurt anyone emotionally, nor does she want to lose anyone. Okay, few things wrong in this statement (right?). Now, she’s in the middle of a situation where she feels she has to choose. I’ve told her on multiple occasions she does not have to do this, that she needn’t to worry about me because I am fine, and really, I am not hurt by the situation because I understand. I still love this woman, and I think it hurts me much, much more that she insists on being with a guy who has treated her unfairly, and has disrespected her more than her cheating on me. It bothers me and it ‘eats’ at me. I am not sure what to even say to her. At this point I feel I am going to lose my mind if I continue with this. I do not understand why she doesn’t realize what she’s doing may be a mistake. She is interested in being with a guy whom has disrespected her in more ways than one, and will probably do the same thing again if they’re back together. Something is not right here. I need some options, because for this matter, I may be running out of ‘em. And my last resort is confronting her and telling her she has to forget about me, and leave me because this situation is ridiculous. I know I do not want to hurt her like this, considering we still care for each other, we had plans of continuing this relationship for years to come, but at this point, I don’t think that will be happening. If she wants to be with him, as much as I don’t want to see her hurt again, I’m ready to tell her to go ahead and engage in a relationship with the guy and not to look back at me, or for me, because I want her to move on from me.
Any ideas?

I gladly appreciate you guys and gals for taking the time out of your day to read this long thread and responding. I thank you, have a great rest of your day.