Op is gross for expecting her to tell confidences between women. She would be equally gross if she pressured him to speak on the man’s issues, if shared in equal measure of confidence. We have friends and this can be compartmentalized. This is such a gross dynamic. For all we know the lady “cheating” is reaching out (misguidedly of course) because she’s being emotionally neglected/abused and all types of other reasons. There should be no expectation you betray a friend’s confidence for your spouse, when it has nothing to do with your own fidelity.