The thing is that, if DPC is trying to make this game even a little bit realistic in terms of what happens when you date/have sex with multiple girls, then perhaps some of them will not react well to the MC choosing someone else over them and this is where the "punishment" would be.
A big example of that would be Jill, someone who really wears her heart on her sleeve and is very sensitive, that if you were to pursue her, have sex with her (possibly take her virginity too), but then choose someone like Sage, she's very likely to be crushed by that, massively so, and seeing that moment is likely to be just as soul-crushing for the player as it is for her and designed to make you feel like shit for having done this to her.
This kind of thing could happen before entering into a serious, committed, official relationship, or could even be the moment when you decide, but I think there is scope and possibility that a "punishment" of seeing a LI be crushed by your choice of another and/or finding you've been with others whilst being with them could happen.