My guess is that W wants to be able to share some problems she has with the M with you in the presence of a C with whom she feels safe. I don't think you need to be afraid of her C, just try not to be defensive.
BTW, I suggest you NOT brush this off:
"*She said things aren’t really so bad, but our main problem is our sex life. (My thoughts: We had a baby one year ago… I hear this is normal, but we need to figure out how to fix this….) *She needs more physical closeness, even if sex isn’t the goal."
W is telling you that she is NOT satisfied with your sex life and with physical intimacy in general. It is VERY VERY hard for women to tell their husbands that they are not satisfied. Really. You have no idea how hard this was for W to say. It is almost certainly only a hint of broad and deep sexual frustration.
So LISTEN. Do NOT assume because she seems to enjoy sex with you that it is really working for her. Indeed, assume the opposite. Assume that for years she has been becoming increasingly sexually frustrated and bored because she is NOT being sexually satisfied and sees no way to get there.
This does NOT mean you are a bad lover. It is really a problem with how women are socialized as sexual beings which leads them to subordinate their own sexuality and act inauthentically in sexual relationships.
I'm just pleading with you, listen to your W closely on this. Don't push her. Just listen and take what she says 500% more seriously than what she says.
Buy some books, some new sex toys. Push her limits and thereby give her space to be more sexually authentic.
DO NOT LET YOUR MALE SEXUAL EGO GET IN THE WAY OF HEARING HER. LET GO OF THE ANGER AND HURT. BE HAPPY TO HAVE THIS INSIGHT AND GRATEFUL THAT YOU HAVE A CHANCE AT A MUCH BETTER SEX LIFE.
