Hi guys, unfortunately I can't follow the thread carefully, so I don't know where you are with the various theories.
After playing the last update I noticed that in the diary of the MC's mother she talks about a man with whom she wants to escape, he would seem a wealthy man, but above all with an initial different from that of the father of the MC, so I believe that at the Eventually it turns out that the MC is not his father's biological son and I think he can be important in the relationship with Jill. After all, we practically had sex with each of the various LI, except her, every time we stop to kiss. I believe the MC may be Jill's brother, and knowing Dr Pincake this means that we won't be able to "get to know" her, leaving the road open with Bella.
Bella is not a serial killer, of course, but here too we have discovered something interesting, she feels guilty for being a traitor, the thing she hates the most, I don't think her husband is missing, I think he cheated on her and she kicked him out of the house, so I expect him to return, triggering a little triangle with the MC.