The Chart explains the mysterious phenomenon of a man who is not interested in sex. Let me save you some time. He’s bored and/or not turned on by what is in front of him.
In fairness, one of the possible culprits listed (biological, emotional, relationship, porn) is actually unrelated to the woman he’s with. I can see medical problems getting in the way of sex. The rest are some variation of she’s just not doing it for me tonight.
Here’s my breakdown of the non-biological rationalizations: