Infidelity and its significance in Conversations with Friends

Part One (roughly, the first half) of Sally Rooney's novel, Conversations with Friends, ends not far from where it began, with the 20-something narrator (Frances) and the 30-something handsome actor, Nick, pursuing their sexual relationship and each fretting in her/his own way about whether it's love or sex, the guilt (or not) about infidelity (to spouse - i.e., his wife, Melissa, and to ex-partner, her former lover and best friend, Bobbi), and about their extremely sensitive feelings. Though one would think from this set-up that Nick would be a cad at best - the unfaithful husband - and a predator at worst, coming on to a much younger woman who's clearly vulnerable and with significant father issues, but that's not it at all: Nick notes that his wife has been unfaithful many or at least several times before while, till now, he has been true to her, the narrator seems perfectly well able to speak for herself, and most of all the two of them are extraordinarily solicitous, constantly checking in w/ each other as to whether one has said something to make the other uncomfortable - whether during sex, in general conversation, or in their many back-and-forth messages. In fact, I almost find it hard to believe in Nick - or at least he's not typical of most male characters which is to say of most males, but, OK, let it be. At points the novel strains credibility - the two are at best reckless in their sexual encounters - for example, many liaisons in Nick's bedroom (it's telling that he does not share a bed w/ his wife) while in a small rental house on vacation in France - and nobody notices anything going on between them? Not likely. Then again, maybe that's part of what's going on; clearly there's an attraction between Nick's wife and the narrator's pal, so maybe they're intentionally pushing Nick toward the narrator (Frances)? There's not a lot of plot development in this talky novel through the first half, and I'm wondering how the ground will shift and the pace will pick up, if at all, in the second half.