Again though, if Jill is aware she has this kind of problem, I don't see her being as comfortable as she was with sharing her bed with the MC.
You're conflating awareness of a problem with acknowledgement that it IS a problem. It's entirely possible that Jill is aware the sleep humping thingy has happened before but believes that it is not a persistent problem (either in ignorance or embarrassment). People can be very good at rationalizing away unwanted truths.
Also, during that exchange it feels like Bella is the one carrying the guilt over whatever happened before. She's the one turns from Jill when they're looking at each, she's the one who gets very defensive when Jill tries to reassure he that whatever happened before won't happen again, and then she pushes the picture of her and James to the floor in apparent frustration. If Jill had done to Bella as she had done to the MC, I don't see why Bella would be so defensive and unwilling to talk about it because it wasn't her fault. The way she acts makes it seem like she feels somewhat responsible for whatever it was that happened between them.
Bella is short with Jill, but IMHO Jill seems to be the defensive one. She's the one who actually brings up "it," and Jill definitely took umbrage when Bella rejects her reassurances.
What that actually means is anybody's guess. We just don't know enough about Bella to speculate usefully at this point. Hopefully that will change soon.
Sure some die hard fans can easily find these thoughts from Bella after lashing out a nerd in the library in ep3, just before the scene that ends with the infamous "I'd have called for help". I've seen a lot of theories about that phrase and also about the Jill/Bella bedroom scene but this one seems to have been forgotten, although it could reinforce some of those theories:
isa "(I did the right thing.)"
isa "(This was for Jill.)"
isa "(Married women don't fool around with young students.)"
isa "(...)"
isa "(They aren't intimate with friends either...)"
isa "(But that...that was different!)"
isa "(It doesn't matter... I've stopped it.)"
isa "(Please, James... Forgive me.)"
isa "(Please, just come home again...)"
isa "(It's been long enough now.)"
The thing I note about this exchange is that Bella makes it sound like fooling around with young students and being intimate with friends are two different instances.
If that's the case, she either fooled around with Jill before she was a student (
so not going there), or she was talking about someone else.