I'm so sorry to hear this. While I do recognise and respect how you must be feeling about all this and would love to say to do what you need to do to feel safe and comfortable with your situation, I also feel something of an obligation for the boy you may potentially be leaving your son alone with.
Do you feel your son has truly reformed? If not, does the mother of the boy know about his past?
Would your son be more or less likely to do something, do you think, with his ever watchful mother looming?
Again I do recognise your feelings. They are very valid and very real. This must be incredibly stressful for you. But if there's a child in potential danger, then (my personal opinion only) perhaps it's worth making the boy and his wellbeing a priority. However that looks, keeping in mind your own safety and wellbeing.
Understand I say this as a victim of long-term childhood sexual abuse. I was told it was just what people do when they love each other. I never had anyone stand up for me. I didn't tell my mum or anyone else because I trusted. No one ever knew. I didn't even find out how wrong it was or understand the damage it did until I was much older. Sorry to be blunt by the way (Mods please do add a trigger warning if necessary - I'm not sure how).
All that is not at all to say the situations are in any way similar or identical. Just the perspective of someone who has lived through my particular situation.
Another quick perspective if you will, I've also been the parent who deeply trusted someone that ended up touching my child. That one is soul crushing and I still can't bring myself to trust anyone with my kids - 5 years later.
If you're really worried I'd strongly consider engaging a licenced psychotherapist - maybe even a specialist in child abuse/trauma etc. They will most likely have more information if not contacts with people in places that can assess and intervene if necessary. Worst case, police or social worker. I'm really not sure about talking to your son or the mother yourself, I don't know either of them, and my personal instinct is to keep your own safety in mind as well.
If nothing else and stepping away is the only option you feel is right for you, then again, your safety, wellbeing and peace of mind matter too.
I truly hope you find a positive and productive way through your situation. That's a real sucky one to be in. I'm sorry for you.
Please do keep in touch with updates if you feel up for it.
