I told her I understand she's frustrated, but that I didn't want to promise something that I couldn't keep my word on, since I'm close with her family (actually, closer than with my own...) SO I tried to valudate and listen but hold my ground.
She doesn't get to tell you whom to talk to or not. If she is so comfortable with her choices, then she's been up front with her family. After all, she has nothing to hide.
Having said that, I would err on the side of saying very little to them about your situation unless specifically asked. You don't want to be perceived by her family as manipulating them to get at her. It also makes you look weak/desperate/controlling to your wife. Talk about sports, the kids, work, etc. with them, but wait for them to ask you about the marriage situation. Even then, vague answers like "I'm doing as well as I can expect" are appropriate unless they ask for specific detail.
They already know about the affair. Involving them in the minutiae of your marital conflicts just makes you look small.
