

I wouldn’t ever.
If he has really changed, he will understand and accept neither of you having any contact. That is the best future for you and your son and he should know that.
On the other hand, for some abusers therapy can be like a training to improve their abuse skills and to hide it much better. And for what should you take that risk? Does he have anything to offer (not talking about material things here)? What could he possibly add to your life?
Worst case, he has not changed or relapses and traps you and your son again in his abuse. And no, a 12 year old usually does not have the facilities to handle abuse against themselves or to prevent themselves from being used against the non abusing parent.
Best case is what? Your son can meet someone who is a stranger at that point. And you can never have a normal friendly relationship to the guy, because the risk of new abuse is always there. So what’s the point?
I would say even contacting you was an act of selfishness. He want to „check up on you“ to fill a hole he has left in himself, not to do you any good. If it was for your benefit, a simple message of regret would have more than sufficed, without pushing for a meeting.
Yeah, but it’s not insider trading. Everyone knows they fucked Medicare up.