I had the misfortune of briefly dating a guy who after several months long distance dating revealed he had abused his step sister when he was 12 or 13. When I reflect on his overall behavior it seems he shared this information with me as a "test".
I was completely spun and had to go no contact just to finish my exams that semester. I tend to try to see the good in all people but I got a bad feeling from this one. Looking back I realize I was flying back to see him after the disclosure & my exams were done and I dissociated in the airport bathroom for over an hour. I recall hearing the automatic flush in my stall over and over. I missed my second flight. He reacted with rage about the delay (I had to fly into another airport and catch a third connection), cursing the airline for not getting me a better connection. I took him to a wedding and he intentionally embarrassed my ex of 7 yrs by adjusting the ex's necktie after I introduced them. Pointless, my ex was engaged to another girl at that time.
I share this to let you know that predators demonstrate red flags in multiple environments. This guy rationalized his behaviors, did not conceal his selfish nature and poor impulse control, and in retrospect, likely shared his history to evaluate me as a mate who would accept such actions in his past with no clear evidence of reparations so that he could feel secure that this history was totally ok. Reading the Overcoming Incest site really drove home the fact that I dodged a major bullet. I likely made the mistake of considering a relationship because he appealed to my guilt and imperfect boundaries. People who overlook the red flags in individuals like this have their own character pathology-- either they too are predators or they are weak and have to learn when and where they are vulnerable to permitting such people into their lives.
We cannot control the abuser and cannot protect all of their associates. Other people who met this guy around the same time also decided to sever ties not long after as he became aggressive towards a gal at a house party when they disagreed.
If you have not reported a person who harmed you, taking action is reasonable. I don't know if reaching out to current partners and associates will be rewarding or demoralizing, and may put you at increased risk of harm.
Just one opinion based upon my experience. Take what you like and leave the rest.
-Ocin