as a virgin I probably don't have much right to give advice for this situation, but here goes anyway;
As I see it, there are three options:
1. He'd like more sex, but he thinks she doesn't want to, or that she'd only be going along with it not not really want it. awww, that's very sweet of him. All that is needed to resolve the situation is for her to tell him what she wants, and he'll be happy to oblige.
2. He simply doesn't want more sex, he's perfectly happy the way it is, and isn't aware of her frustration. I guess that doesn't really explain why he's hard and does nothing about it, though, or why he doesn't at least touch her when she's sleeping in the nude. They have to come to some kind of compromise. Maybe he can have a little more sex than he usually would, and she can have a little less? Or maybe he can find other ways to give her pleasure without having actual sex.
3. why has nobody ventured to ask whether maybe he doesn't have sex as often because he doesn't find it fulfilling? She said the sex is great, but is it great for him too? Are we blindly assuming that men enjoy sex, any sex at all, period?
That does not mean that she's being selfish or anything bad like that. Since she already said that he's shy, maybe he's so shy he wont even tell her what feels good in bed, and hence she has no way of knowing that he'd prefer a different technique, or that ear licking drives him mad. Maybe he has a secret fetish that he's too ashamed to explain. Everybody has the responsibility to tell their partner what brings them pleasure, otherwise they wont know how.
Please keep us posted, Sweetee
Best Wishes,
-tiay