The conversation with the woman honestly needs a total rewrite. I wasn't entirely clear on how to do it at the time, and it's a scene I really struggled with.
For the story's sake, I had to find a way to keep her out of things (the story is about the boy and girl, after all), in a somewhat believable fashion—the result, was lackluster and uncharacteristic, just too sociopathic as
Settum said (though, the way it currently is, does fit for an alternative path I have planned in the future, with a more "stern/proactive" PC character).
Now, I've had time to think about the conversation (I've been unhappy with it for a while), and come up with a hopefully better idea of how it should go down:
He is supposed to feel hurt and to not want to absolve her of her "sins", and he is also wary of her, her marriage is falling apart, and who knows if her turning over a new leaf will last?
He thinks she basically wants to swoop in now to make herself feel better, and that it is not out of genuine regret/concern for them. And obviously the relationship between them isn't great in the first place so it's hard for him to trust her motivations (again, also because he feels hurt by her, and doesn't want her to feel better).
On the other hand, he's also afraid that his reasoning is self serving, and that perhaps he has other, hidden motivations. And he's uncertain what the truth is, and he's kind of scared about the way he is acting, and he wonders if he was right to keep her away.
In the end, as you said, he puts it out of mind since it already happened, and that he has all the time in the world to think about it. And that if it turns out she truly did change, that he can still go back on his decision.
This discussion has given me the motivation to go and rewrite this entire scene finally, hopefully in a better way. It's... not easy to write this well though, so hopefully it turns out okay, or at least, better than it used to be. I at least think the motivations described above work out better than the way it's written now, better fitting his characterization.
And to somewhat keep swinging between, nothing will ever happen and I will take control of her and mixing in some "looking and thinking is harmless". But slowly corrupting himself.
Yes, this is basically what I had in mind as well, just hope I can execute it well enough in an interesting fashion.