I disagree, to a point. He's not an asshole for considering it or being tempted. And he wouldn't necessarily have to be an asshole for letting it go as far as it has. But he is an asshole for hiding it from his wife, especially given how completely open she's been about the progress of her own relationship with Jenny. I doubt the game's going to punish him all that much, because I don't think it's that sort of story, but he's being offered a (semi?) permanent threesome on a silver platter, and he's screwing it up.
The dev said they had the revelation scene planned out from the start. As a writer (not of games), this is one of those instances where I look at something that sounded amazing in the outline stage, keep trying to figure out a way to force it into the narrative, then finally accept that no matter how much I loved it during the conceptual stage, it doesn't work anymore given the existing story. I hope to be convinced otherwise, though.