Self-fulfilling NTR!
Now, I think it's very likely Akito and Inuka were just hanging out as friends. He's very peeved to have been one-upped by someone he considers beneath me so he's been on a quest to understand what those girls find in him and to get back his mojo.
Akito is not only one of the potential 'witness' but she also have the same curiosity for this lifestyle of casual sex since she did it with Gotou and that seems to be the kinda girl he's into. So it makes sense for her to get some answers from another if not a more typical fuckboi like Inuka.
Mind you, i think it was already a slippery slope and both were likely to bone, as misery needs company, but Gotou showing up with another date (from Akito's POV) was the last push here. With this encounter, they both could hurt his ego and alleviate theirs by making him jealous/appearing fine and wanted without any of them.
Gotou is really not built for that life. He made the mistake to ignore the President, when she hinted very clearly that she wouldn't take it kindly to be left hanging on their date, so of course she ruined his (pathetic) moment by throwing oil into the fire.
Also, why is he acting like if Akito is his girlfriend? If he liked hooking up with her, he should have clarified their relationship, especially knowing that she was in love with him, instead of spending weeks jerking off on his own. You can't complain about someone stealing your girl if you never secure the bag!
He's so wishy-washy he doesn't know what and who he wants, so he's going to lose everything chasing them all this sloppily.