On the Bella-only route, I can understand Jill's initial reaction of surprise, but I'm wondering why she still avoids Bella. I have my thoughts on this, some of which include her being upset that Bella is cheating on her husband, or that perhaps she thinks the MC would have given her more of a chance if not for Bella, but I expect all will be revealed in Episode 9.
I think it's closer to that. I think she starts to get worried after you play the song for them at Bella's and you remember it's her favorite song. She also gets snippy with her for not letter her know that you "moved in". Overall If you are just on Bella's route I think it's more of her being hurt her best friend was hiding something like that from her. Maybe even a little inferior, for lack of a better word, about her not being chosen.
On the Bella 'only' path, I think Jill is upset/disappointed due to:
Jealousy - She was into the MC even if you never start anything with her.
Betrayal - Bella is Jill's best friend, yet she's been keeping her relationship with MC a secret from her. Despite Jill telling her about her interest in MC, and Bella pushing her to pursue it if she's come around.
Python:
if ep3_bella_came_around:
...
ji "And? You like him now?"
isa "No. Not at all."
ji "But?"
isa "But he's not all bad."
ji "Not all bad?"
ji "You know, that's the nicest thing you've ever said about a guy."
isa "..."
ji "I think you might be right."
isa "Good. So, go ahead."
ji "Go ahead and...befriend him?"
isa "Yeah, that or date him. Whatever."
ji "Date him?"
I don't think it has anything to do with Bella cheating on her husband. We don't know that actually happened, and even if it did Jill has been fully supportive of Bella after whatever prompted his disappearance.
They do talk about it though in the scene when they're both in bed together before she makes her way to the couch, so obviously something between the two happened, even if it was just a kiss between them.
I think that the husband was frustrated due Isabella´s coldness with her. Then, for some reason, one day Isabella and Jill were "fooling around", the husband caught them
Bella & Jill never fooled around. That was a theory pushed on wish-fulfillment misinterpretation of the scene where Jill stays in Bella's room. There was never any evidence to support it. The only thing we can confidently say about their argument is it has something to do with James departure, and Bella hates talking about it. From Jill's ep7 and ep8 lewd scene it's obvious she's never been intimate with anyone.
