Don't forget that during the date with Jill, the MC tells her about his life, the death of his mother. They then share a fairly intimate, romantic moment for the rest of the day.
(if I'm not mistaken, this is also what happens with Sage)
In fact it's not really the fact that we go to see Sage that blocks the road with Jill. It's not her who reacts like a selfish bitch, it's rather the fact that by going to see Sage, you don't experience a romantic and intimate moment with Jill which brings the two very much closer together.
Reasoning in terms of game, by going with Sage, we lose the opportunity to earn XP with Jill, and in the end, we miss this XP to level up.
(if I'm not mistaken, this is also what happens with Sage)
In fact it's not really the fact that we go to see Sage that blocks the road with Jill. It's not her who reacts like a selfish bitch, it's rather the fact that by going to see Sage, you don't experience a romantic and intimate moment with Jill which brings the two very much closer together.
Reasoning in terms of game, by going with Sage, we lose the opportunity to earn XP with Jill, and in the end, we miss this XP to level up.