Bella and Jill, as I said Traditional relationship approach. You constantly work toward for it and each things move it one step forward, some decision is more important than others.
First you have to work toward to achieve that Jill likes you, once you achieve this, that is when she invite you, but if you reject this , then why should Jill not care about this rejection?. think of it as like an already existing Branching.
I might be wrong, but Bella has a similar "check". If you reject her help for cleaning your room, you shut down the Bella path.
This system alone is not bad at all, its actually realistic. You actively have to spend time and invest to the girls in order to achieve something with them.
What is complicating it, unnecessarily, is the Affinity system. However I do understand why that is exist, because the Affinity system also works beyond just the love storyline .
all in all, Jill have a path you have to follow, and if you deviate from that path, in a key moment, then you lost it.