W: Well I guess so, I DID wait for you.
M: Yes, and I appreciate that a lot.

W: Well, that's the point isn't it...a popularity contest to see who can win over the girls?
M: (and here is usually where I get very upset) I certainly can understand why you might think that, because I have been really bonding with the girls these past few months, but I have to tell you that I don't appreciate the implication. Throughout this whole ordeal, I have never said a bad word about you, but still continue to tell you that you are a fantastic person and a great mother. The implication that I am somehow trying to turn them against you is really unfair.

"I don't even need to be here, you guys don't need me."
"I can understand why you may feel that way. But know this, I need you, the girls need you. We are not a family without you."

Rob,

Thanks for the excellent examples of how to validate W's feelings and diffuse potentially difficult situations.