When does Jill spot MC fucking Bella? I do know there's a scene of MC fucking Bella on the table but never do I see Jill in it. Other than that you're just bringing up hypotheticals here. Jill isn't even on the DIK path so she doesn't matter. Neither are Maya or Josy. Sage was more angry than anything that Chad cheated on her while completely rejecting her advances. Then she proceeded by cheating on him.Sure, go get spotted by Jill as you fuck her best friend on the kitchen table and try to claim again she doesn't have any problem with the MC sleeping with someone else.
As pointed by others, the only main girl who might not mind you sleeping with others is Sage, and even that is debatable considering how she exploded over Chad cheating on her. Every other girl will reject you, either if she learns about your sleeping around, or won't even want to form a relationship with such MC to begin with. It's a joke to claim this somehow doesn't prevent the game from just allowing DIK MC to sleep with everyone and not a single of the affected girls minding such development.