Uff.
I'm doubting they did anything, and I sure hope they didn't - because I guess there's the proof that Arimura hasn't changed from the idealising stage. I bet that happens in a few chapters time: "D-did we... do anything?" "Of course not, I'd never allow it - the Kusanagi-sensei I know wouldn't have a drunken one night stand" or something.
Well... if she hasn't got over her focus on the ideal and isn't acknowledging the real Kusanagi yet, hopefully that's what this arc does - gets Arimura to change without her and Kusanagi getting together...