What I mean about marriage seeming like a prison... For example, if the wife is no longer interested in sex and turns him down all the time, the husband can feel like he's in a sexual prison. He might suddenly realize he has no socially acceptable ways to have sex with anybody at all. He doesn't want to force himself on his wife. If he goes outside the marriage, he's cheating. If he divorces he loses a lot and it affects his whole family, and it seems like divorcing for just sex is cheap and selfish. And then he thinks of single people, and how they have sex all the time with a whole bunch of people and it's totally socially acceptable -- stuff he can't do with anybody. Marriage is supposed to represent the most socially sanction sexual relationship there can be, and instead it's the exact opposite. He's in an invisible prison.
I think there are all kinds of emotional and ego variations of this feeling of feeling "imprisoned" in your marriage. That can result in a feeling of slow panic, and so the husband feels he needs to "bust out of prison" while there's still time!
