Truthfully, I did not (and do not) intend to do anything or say anything. The problem is that my sense of cosmic justice is offended. I know the truth will out eventually, H will have to explain himself, and people will put two and two together about the affair. I'm just impatient for some consequences.
(In talking this over with a friend, he actually pointed out that there already have been plenty of consequences - H is barely part of his son's life, has alienated our mutual friends, trashed his reputation, endangered his career, surrendered the assets and wealth we shared, and has to live with his bad self. Touche!)
Once I allowed myself to come to that conclusion, I realised my desire to tell was fed by an underlying desire to regain control. And that recognising this emotion, and choosing not to act on it, is actually an act of positive control. It restores my sense of agency just a little.
So I dealt with that, but the anger wasn't going away. What else was bothering me?
It's the suspicion that H is taking S back to his house for morning visitation without my knowledge.
I was upset about that for a number of reasons - that H is breaking the rules, going behind my back, giving the middle finger to my custodial rights, demonstrating gross entitlement at the expense of S, and generally taking the opportunity to stick it to me by acting out some form of juvenile rebellion.
I stewed on this for a while. What it boiled down to (lots of cooking metaphors here) AGAIN is my loss of control.
Realistically: - It's only a few hours - S is not in danger - I can't enforce it even if I did raise the issue
Therefore I'm circling back around to my original conclusion which is to do nothing and say nothing. And again, by choosing this action of inaction, I AM in control of the only thing I can control, which is myself.