Oh just give up on Chizuru and pork the real girlfriend already.
Listen Kazuya... this manga could end in a few chapters if you just gave up your naive idealism, abandoned the petty infatuation with Chizuru, and just accepted this girl who earnestly believes you're the one.
Yeah, there could be trouble with the grandmothers. It happens. But you could get hitched with this girl, lose your virginity, and a few years down the line you could be taking over the family business with a second kid on the way and an instant stable marriage with the same girl you lost your virginity to.
Thing is... you have no appreciation for that kind of stability and how rare and precious it is... do you, mr protagonist?
No... we're going to see this relationship go down in flames despite the chapters dedicated to it. There will be bullshit with Mami and more naive chasing after Chizuru, and probably a few more chapters with that shy girl... And there will be more accidents, more stupidity, more contrived drama, and lots more pointless lies.
And for what?
Most likely a bittersweet ending at most.
But most guys don't get to be with the fancy girl. The most some guys can ever hope for is to be with the girl who wants it the most. The most plenty of guys can manage is to die alone. Just end this nonsense already...