I honestly don't know what you guys expected to happen to Sage's character in this episode. I get that a lot of people (me included) wanted some cute scenes like the ones in season 2, but this was not the episode for that. One small flashback and a big party, that's all we got for the MGs.
There simply wasn't enough room for character or relationship development. Josy and Maya was the only route that felt like something actually progressed, but that's because they had the "advantage" of having the MC's declaration scene postponed to this episode. If that wasn't the case, I'm sure a lot of people would be complaining about lack of development for them too.
But back to the subject, Sage has always been a girl who likes to party hard, get drunk and all that. So it should come as no surprise that she would behave accordingly. On top of all that, now she's finally in a healthy relationship with a guy who she can finally be herself and explore all her sexual desires that were repressed for the last 2 years. And what better place to let loose than a big ass party? That fits her character perfectly and shouldn't be considered as regression.
Sage is no Jill, so you will never see her talking about family in the middle of a fucking Halloween party.
I mean, this scene says it all:
For the comments I've seen here since release, it seems that some people expected Sage to be all cutesy with MC during the party, and that's simply absurd to me. Not only would that feel forced, it would also make no fucking sense for her character.
They didn't even go on a date yet, so a sudden change in behaviour just because MC declared his intentions with her in the last episode would just feel like some big steps were skipped. And even still, she still had some cute moments in the party here and there, they just weren't as abundant as it was for Jill for example because, like I said, it's not Sage's style to do that in a party. In her few moments of sobriety (Burkes visit and the flashback) she was still the same old Sage from season 2 - caring and sweet.
I understand the people that felt disappointed with her path in this update because of the overall sexual tone. But to say that her character regressed and/or is ruined because of ONE episode is just overreaction. If this continues in normal episodes however (I don't think it will), then I will be disappointed.