I want to tell him how he and the love of his life will slowly fall into a routine, how the sex, while still perfectly fine, will become commonplace enough that it won't be unheard of to postpone it in favor of a television show, or a late-night snack (3.10)
Here we see the contrast between the passion of a young relationship and the predictability of a long-term one. It's easy see how the monotony of Jen and Judd's sex life relates to the other issues in their relationship. As the sex goes, so goes the relationship.
"Why is it so hard for you to accept that your mother is sexual being? Do you think you were immaculately conceived?" (10.16)
Okay, so Hillary's habit of talking about her sex life is probably super embarrassing for Judd, but it's probably been more beneficial to her kids than not. Imagine how messed up Judd would've been if he came from a home filled with sexual shame.
For one thing, you've become a bit too efficient, you've learned what works and what doesn't, and so foreplay, entry, and orgasm can often be condensed into a five-to-seven-minute span. Good sex requires many different things, but in most cases, efficiency isn't one of them. (19.26)
Again, we see how Jen and Judd's sex life is tied to their personal relationship. Neither of them is willing to be present for the other while they are making love—just like they aren't willing to be present for each other after Jen's miscarriage. They might as well be taking care of business alone, if you know what we mean.
"She cheated on you, and I know that hurts. But it's only sex, Judd, scratching an itch. We've been programmed to attach far too much significance to it, to the point where we lose sight of everything else. It's just one tree in a thick forest." (22.9)
Ouch. This is not what you want to hear after your wife cheats on you, but that doesn't make it wrong, exactly. Don't you think the world would run a lot more smoothly if people didn't feel the need to freak out about sex?
But when your wife spent the last year of your marriage going elsewhere for her sexual gratification, it's only natural to have some performance anxiety. (31.100)
Jen's affair with Wade has left Judd struggling with his masculinity. Things are made worse by the fact that Wade embodies all of the masculine ideals that Judd fails to reach.
The sex is good and bad as first times tend to be, like a play rehearsal full of missed marks, botched lines, bad lighting, and no calls for an encore. (31.104)
Real sex isn't like the stuff portrayed in the movies. Like any relationship, it's much better with an emotional connection between two people. No matter how much Penny and Judd want to be with each other, they still don't know each other well enough for good sex. (But at least they don't know each other well enough for bad, right?)
"In my limited experience, women rarely leave because the sex is bad. The sex becomes bad because something else has gone wrong." (31.112)
Five dollars to Penny for being the most insightful character in the book. She's able to intuit in one conversation what Judd hasn't been able to figure out in the weeks since his separation: that he can't actually blame the sex for the failure of his relationship, no matter how much he'd like to. He really needs to blame himself.
You can see your parents have sex, you can see your wife in bed with your boss, and, still, none of it packs quite the same surreal punch as seeing your mother kiss another woman. (45.24)
Why does Hillary's lesbianism shock Judd more than any of the other (many) bizarre sexual encounters he's witnessed? Probably because his mother's sudden change in sexuality throws Judd's whole conception of sex upside-down in a way that an affair doesn't.
"I'm seventy-two years old. I drink my coffee alone every morning, and fall asleep with the TV on every night." He smiles. "There are headaches, and there are headaches." (45.31)
Here, when Judd tells Peter that he's better off without marrying Hillary, Mr. Applebaum gives Judd a glimpse into his own life: an old man still chasing after pretty women. We'd be terrified, but Judd seems to find it comforting. No matter how old he gets, he'll still want to make it with the ladies.
"It started as something purely surreal and physical." Mom speaks in her TV voice [...] "But Linda and I have been so close for so long. It was only natural that a physical relationship would evolve into something more. (47.48)
Hillary and Linda's relationship is the embodiment of Hillary's freewheeling views on sexuality. However, it's the two women's longstanding friendship that transforms a purely sexual relationship into a truly romantic one. Maybe this is Judd's problem: he focuses on the love and expects the friendship to come later, when really he should be focusing on the friendship.