A key thing that Michele doesn't talk enough about is how to manage conversations.
You don't have to talk about something just because she is pursuing that. Casually and subtely change the subject.
I have tried the following successfully too :
"Considering where we are at right now, I don't think that would be a constructive discussion for us both. I would like to talk about this further, but I don't think we are ready for that right now."
Just chum around with your child as often as you can. Just look at her as if she's on vacation or something and have both of you wave to her and say "bye mommy" and fun casual things like that.
It will endear you to her as the father of her child. I am actually surprised she's not more vocal about protecting him right now...not a lot of maternal instinct surfacing there.
I am wondering if her parents calling the OM's parents and telling them to get their son to stop harassing their daughter. I think as long as you don't appear involved, pressure is a good thing. If you have the card, play it.
Maybe his parents don't care about the damage he's doing..who knows...I would be mortified if my son was violating a home like that. Phil McGraw says its no better than breaking into their home and stealing their things.
Anyhow, you are in a good spot B, just keep up the reading, that was the area you were falling short on. Michele points out in her book that you should read as much as you can on building and healing a marriage.
Not Just Friends is a good book to get too, by Shirley Glass. There are many good books out there. After the Affair is popular too, though I find it is way too sympathetic to the unfaithful spouse. Its also written in a voice that addresses the unfaithful spouse directly...so you may find it hard to stomach, but ATA has lots of good things to say though.