do I have an obligation to warn someone about thier current boyfriend?

back story: there once was a guy I was "hanging out with." we were both drunk one night and crashed on a friends couch. I don't remember much but the sex was consentual so long as there was a condom. It quickly became nonconsentual when I noticed the used condom was in his hand. He stealthed me and it was after the fact when I noticed. Fast forward 3 months and I tested positive for chlamydia. I was in a new relationship at the time and it was hell. Fast forward almost a year and I find out he gave someone else something, that was unfortunately more permanent and this was several years before we hookef up. I recently unblocked him on Facebook and I can see he's in a relationship that looks happy. I feel like i need to reach out to her. If he didn't know he wasn't clean before me, he knows after me. What if he tells he's clean like he told me? He will keep committing sex crimes until someone stops him.