The Dev explained why it made sense. Really do not see it as a stretch. We also are not privy to how the story will unfold. There were really just two paths - Loyal with minimal sharing and sharing (cuck). I believe I was on the sharing path because I wanted to see the most content. There was no “Netorare” path in a pure sense. The dev forced everyone into the hotel room to create a conflict. Don’t see the problem with that it is a common device in story telling. What you did in the hotel room is up to the player. I think some are simply upset there was an option for her to veer into Netorare instead of asking permission first. At least that’s my take.
A lot of people are landing in the same place you state in your (second to) last sentence there despite plenty of the people who are unhappy explaining why they are unhappy and none of them (that I saw) saying it's because there was no permission given before fucking Pat.
If Kathryn and Pat fucked, that's player choice (and with two options before then to shut down what was a pretty obvious path towards it). The issue with the storytelling is the pretty ridiculous series of events that led to Kathryn and Pat being alone in a motel room in the first instance. If you're playing a loyal game, the argument and storming out seems really forced, there's talk from Kathryn about maybe coming back from Spain on separate planes, and it's just out of keeping with the game you might have been playing up to that point. Fair enough if you've been playing the game with both MCs getting their fill of other characters, but not every player and every save will have that history.
And then of course there's the very weak plot contrivance of "That's a lot of rain, maybe we should get a motel room instead of continuing in this car that is clearly up to the task of driving in sub-optimal conditions."
A few methods have already been posted by various people, but another pretty easy save for this path would be for Kathryn's call to actually get through to Luke, and for her to explain that they got caught in the storm and have had to stay in a motel, she's sorry they argued, and she loves him and will see him in the morning.
So yeah, it's not even about Kathryn fucking Pat (which, once again, is player choice), but that they should never have been in the motel room together in the first place, unless you've been playing a less than faithful save up to that point. And of course, the other complaint some have had is that it's suddenly all NTR and no NTS, which is again not an argument for asking for permission first, but an argument about the overall content of the episode, especially when there were sharing opportunities that were not taken (by the dev), and would always have been taken in previous episodes.