-live in an open M -allow a third party to enter the M
Then you turn around and offer her coffee. Do you see the disconnect? It is a Wet Noodle moment...not the quiet, strong, and no-messing-around husband.
It is NOT your job to show her what she's missing out. Just do it. Pull back, go dark, stop being her H for you are not her H since she's turned her affections to another man. Then she will see the contrast.
Be scarce tonight. Get out of the house. Do whatever you need to stay out...go to the local pub or something to occupy your time.
You are not the kind of man that will lie down and lick the lineoum floor. You are a quality man who won't take chit from W.
