Further to my last post - and bear in mind I'm thinking this through for the first time as I go along - this is hypothetical speculation, a thought exercise.
What happens if my agp ex is in a toilet cubicle in the ladies', and someone goes into the cubicle next door?
It's not specifically me having a piss that's lodged itself into his psyche. The sound alone triggers an automatic sexual response in him, and this response is getting stronger. This is largely not within his conscious control (though he can of course take steps to stop or slow this progression if he recognises a reason to do so).
When the person in the next cubicle has a wee, he's going to be aroused whether he actively wants to be or not.
He could attempt to fortify his mind against this response, but if there is no shame attached to his presence and no one is allowed to call him on the fact that he's getting sexual gratification at the expense of unwitting and unconsenting others, he's unlikely to bother telling himself this is weird. He's just going to roll with it, because there are no consequences for not indulging.
But it's all cool, yeah, 'cause no one's getting hurt, right?
What happens when he exits the cubicle at the same time as the occupant next door, and realises she's ten years old?
He's then got to deal with the cognitive dissonance of knowing he's just been sexually aroused by the bodily functions of a child. He knows damned well that's sick, and he knows he can't be sick because everyone's so open-minded and tolerant that no one will tell him the truth.
What does he do with that cognitive dissonance? How does he resolve it?
This scenario does not end well for him.