Dalli wouldn't be Dalli if he didn't analyze it.
It might not have been laziness. I don't know if this is canon, but in my through game Isabella mentions twice that she loves Jill.
Once just before the second tennis match, after Isabella asked the MC if he was jealous. This is in EP7. In my case, she doesn't take off her ring at the end of EP7. In EP8 after the recital, Isabella gives Jill a rose. A single red rose, the ultimate love symbol. In the Rooster Cluck about the recital, Isabella writes again that she loves Jill.
Maya said to the MC in EP1 so she pretends to have a boyfriend because that keeps away the guys who were interested in her. Isabella, Jade and Stephen arrange to meet in EP1 with Isabella bringing the wine. In EP3, Jade told Stephen that Isabella was naturally in love because she was wearing a wedding ring. So the meeting took place and Isabella did not have sex with Jade and Stephen. The wedding ring worked. Stephen doesn't give up, though, considering EP8. In EP5 it is implied so Jill and Isabella once spent a night together. A common known theory, not from me, but I agree with it. James leaves and wants to divorce Isabella or they are already divorced. Doesn't really matter. But Isabella wears her wedding ring to keep guys away.
In EP2, Isabella gives the MC a chance, but she only does that for Jill. In EP3, the MC wants to pay for Isabella's dinner to make up for screwing up her date in EP2. Isabella insists it wasn't a date. In EP3 it is canon for Jill and the MC to have a date. After that we get 2 decision presented by DPC.
Isabella is in love with Jill, but can't show it openly to Jill because she is Burgmeister and Royce's teacher and also doesn't want Jill to be judged for having a lesbian relationship. That's why Isabella doesn't want to talk about what happened between her and Jill in EP5. It's not about James. Isabella's concern is for Jill.
mc: "I figured she felt the same since she was being unfaithful to her husband..."
mc: "...which, of course, is a very big deal."
mc: "But if I had known the real reasons to her tears..."
mc: "...and to her persona..."
Isabella is crying because she is cheating on Jill, not because of James.
mc: "I wouldn't have kissed her that night."
Zoey doesn't want to tell the MC so he is a fantastic kisser because she doesn't want the MC to become an idiot. Isabella falls in love with the MC in the library through the kiss.
mc: "I would have called out for help."
The MC, when pursuing Jill and Isabella, will not be able to avoid hurting Jill or Isabella. The bad part is so Isabella can lose everything. She lost James because of Jill, she can lose Jill because of the MC, the MC because of Jill, and eventually maybe even Jill and the MC. It could be so that Isabella loses her grip on life because of this.
If the MC does not pursue either of them and the MC is just a good friend to both of them, Isabella and Jill will find each other.