Assisted Suicide.
People want to empathize with the MC because one should never EVER do something stupid for love...Ever...Never...
Okay, that might be true, but regardless of the reason when you KNOW why someone is doing something and still do ABSOLUTELY NOTHING then it's as close to assisting them in their madness as telling them to do it yourself.
Nobodies right in this manga and while I agree she shouldn't coddle the blonde after being a dumbass there was no real reason to stab and twist the blade by going "Yeah, fuck you bitch." I wouldn't be at all surprised if this new chick is some super obsessed Sister-complex Onee-san of the blonde plotting revenge through a very elaborate scheme against the MC.
Because as it stands she's still doing the same thing as previous. Noticing someone's behavior yet doing nothing but over thinking it instead of trying to clarify things directly. Going with the flow just to say it's the fault of someone else when it all goes downhill is blame-worthy just as much as fucking multiple people to get someone to notice you.
I actually like the MC but to say OH she's perfectly right about what she did is a bit sadistic.
"Oh, she likes me eh? Let's see what she does cause I kinda like her too." Hahaha, what?
Oh, are you saying she didn't realize it till she was already fucking 2 guys? I can't really believe that's true.
I don't really sympathize with the blonde but I ain't gonna bash her either, she could have just as-well slept around with different females and the only thing that would've changed is that she wouldn't have gotten pregnant. Could've raped the MC. All of these choices are dumb as hell but she just chose the worst of them cause the consequences were a little TOO heavy to bear.
If the MC would've did something as simple as approach her and say "You need to stop." then I wouldn't see her as a jerkass. I'm already paranoid of the new girl she seems like the Mature, Sadistic, and Conniving type. MC's REALLY about to get it.