I know that some people say Kit's turn to 'incel-dom' came out of nowhere, but I do have to point out that Kit was revealed to the audience as someone who had manipulated his way into Jentry's life for the purpose of killing her pretty early on in the season.
The show does a lot to soften him and explain his perspective after that, and his flirtation with Jentry was cute, but 'willing to murder someone they don't know who's done nothing to harm them for their own gain' is a pretty big glaring red flag about a person's character, or at least moral compass.
Compared to that I honestly don't know that the behavior we see after Jentry rejects him is even worse than the baseline the show set in that episode.
Also the show tells us that Kit has ended up absorbing the qi of (killing) most of if not all of the humans he made a connection with before Jentry. That's the show giving us some very clear warnings about how Kit tends to take rejection.
I think because the behavior he shows in those last episodes is much closer to actual bad situations viewers may have been in or might encounter in real life it seems like he's taken a sudden turn for the worse, but if he did take a turn it was right back onto the road he'd originally been driving on. The situation with Jentry was clearly the detour if we take into account what the show tells us about what this cycle of rejection usually looks like for Kit.
If anything he's at least completely taken the option of killing Jentry to get that soul off the table at that point so in some ways he's improved.
