There're no immediate game overs in such type of games, it's not a FPS or RPG or something like that. But you set up MCs future possibilities as well as fuckups and potential good/bad or "neutral" endings by making particular choices during your playthrough. And I can't expect nothing positive from casanova playstyle and rejecting the "primary" MGs - both J&M and Jill.
Knowing who is the author of this game and what's his previous game was like... You're quite brave and optimistic in your assumptions and fantasies.
Despite the fact that I trust his words that BADIK will not be as gloomy as Acting Lessons, but this does not negate the fact that his games are not like other games of the genre (or at least most of them). This ones are not about building a harem with missing some lewd scenes and galleries as a maximum punishment. It mostly the opposite.
So in the best case, this will lead to the need to make a choice again and finally and irrevocably break someone's heart. Admit, to continue it this way and then, for example, reject Bella or reject Jill second time is very low and mean, especially when you know that they are best friends and meant a lot to each other. This is what this false hope answer and kiss will set up and lead to later. Their friendship and importance to each other complicate this situation many times. So, DPC made a possibility to fuck up once, and then you're able to multiply your fuck up twice. Profit.
I bet, he is preparing something similar for J&M rejection scenario too. Since even Jill breakup was made as flashback, while J&M case is a realtime hell during whole party.
You can kill (literally and figuratively) not only with fire, a bullet or something else, but also by breaking someone's heart, betraying someone, taking away and destroying the most valuable thing that someone has or had, especially when it comes at a very inopportune moment for a person. And with proper directing and writing of such scenes and their consequences, the death of some character can be as severe as the consequences of a broken heart, betrayal and meanness.
When a game makes you feel certain feelings, when you have favorite characters, some sympathies and attachments, then that's how it is.