only devs can answer that and they won't. we don't even know where she's gonna stay and it's been speculated that if breaks with her then she might be opposite side if there'll be lawfight on hotel.
The opposite side has the lawfirm the MC used to work for, the younger guy is the one that took the MC's job.
Pretty sure Nicole's firm won't work with them.
So, what are the benefits (or drawbacks) to a bad relationship with Nicole (girlfriend)? Does it push her into something, or just clear the decks for the MC to stay at the hotel? How does a good relationship benefit the MC?
There isn't going to be any NTR or what have you. A bad relationship with Nicole is the Mc breaking up with her and her leaving the game.
Good relationship is just for those that want to stay with the girlfriend.
There are some girls in the game not looking for full romance, it's only going to be a summer fling like the twins are probably in that category. The MC will go back to Nicole when the summer is over if he's on any of those routes.
If you want the MC to start a new romance and stay at the hotel after the summer is over then you'd have to break up with Nicole.