Sounds like there may be something more going on. Why is wife acting with seeming animosity towards husband when for so long she was a good sexual partner? Affair? Anger over something else? Generally dissatisfied with marriage but afraid to admit it?

I personally feel that cheating would be bad news for a monogamous marriage.
If HHNRW wants to stay with his wife, I hope that their is a way for him to rekindle their sex life. Maybe see a sex therapist? Take his wife on a sexcation? Depression or birth control could be reducing her libido like you said. If by all means she is done with sex, I think he should end the relationship and move on. Sex is super important for me, along with many other factors. No sex= deal breaker. 15 years of marriage is a long time but without sex is it not just a friendship. If the wife does not want to do this with her husband, it would be ideal for her to allow her husband to seek sex elsewhere. However this is not the case and I feel like being honest in a relationship is most important to live a healthy and happy life.

Um, yeah. Why does it seem to assume that only "depression, a libido-killing reaction to birth control, a hormonal issue" is the only thing to be ruled out on a female before setting out to justify cheating. Maybe it's distrust from picking up that he wants strange or disgust that he sits in front of the xbox for 12 hours straight. It's the hiding shit that kills marriage so if you want to fuck others mayhaps put it on the table or bail. Chances are if there is honesty and work is divided, the wife is gonna fuck him upside down and sideways, or maybe she will with someone new too.

Is he really complaining about sex 1 to 2 times per week? And he is summing this up as "pretty much stopped"? That is a grand case of hyperbole that makes some of his assertions a bit questionable. It sounds like this is not a question of frequency (and I am wondering how this guy has time for all this sex?) but about the enthusiasm that is lacking now. How about a marriage counselor? They can help with relationship enthusiasm. And maybe expectations the couple can agree upon.

Is the cheating supposed to make it so the guy can stay in his otherwise great marriage? Because lying and sneaking around is going to ruin that 'otherwise great' part and then the WHOLE thing can go to shit, not just his (high) sexpectations. Jeez, maybe the wife just wants a freaking break!