My issue is not that they got angry over it. My issue is that it's jarring that they got angry NOW of all times over it. It's not exactly a series that's based in realism. The relationships are so paper thin, there is no real depth to any of them. Both the novel and the manga are full of fan service that sometimes even seems out of place for the situation they are in, but the author has done a relatively good job at letting us, the audience, go with the flow and not question any of it. For the author to suddenly make the girls act this way over something the MC does all the time? How are we supposed to take it? It's not like MC has shown any loyalty to any of the girls in particular, and we only have negative opinions about the girl in question only because the author let's us see into her inner thoughts. There is no reason for any of the characters to hate her, or hate him for getting it on with her. Like I said before, where did this divide in the group come from that now a girl from outside the group is off limits? The two sisters, the ojou-sama and her bodyguard, and braids girl were not originally from the group. Where is the jealousy for them at? It's inconsistent...and to makes things even worse, there is at least one other person in the group that knows MC did nothing wrong, and he was being attacked against his will, why is this misunderstanding even a thing? They are usually a pretty competent group, and most of the members are relatively smart, this is just them being dumb for no reason at all.
