Have you considered the possibility that maybe she just doesn't like having sex with you and/or that she is having an affair?
Yeah, this could've been put in better terms, but I do like your direct approach, it's a breath of fresh air in today's world. However, your post doesn't really provide a lot of help. It's no secret she's not into sex as much. It happens to be the reason WHY he supposedly whacks off too much. If she is having an affair, she's got some balls to tell him to cut down on his jerking off. At that point she deserves a roundhouse kick in the face, followed by a warm blast of gooey-man goodness.
But in all honesty, a woman who enjoys a good game of Yahtzee and calls it a night is seriously NOT having an affair.