Sweet mother of god, this manga is killing my brain. Riri wants to date Tarou and lose her power, but she does care for Eve. Tarou wants to date Riri but he is so close to Eve. Dating Riri would make him lose one of his closest friends (and mild romantic partner). He like(d)/(s) Ebino too, but dating Ebino would cause Eve pain and anguish and he would lose Eve. From Tarou's perspective, if he were to get rid of Eve through either of these means, he would essentially be killing a concious being who genuinely loves him.
As such, Tarou is making the choice to fix Riri's zombie sight and burn his bridges with both of them. That way he could never fall in love with Ebino and cause Eve pain AND he could never fall in love with Riri and cause Eve to turn to sparkles.
Him acting like Riri is a guy is just to keep status quo. Partially because he doesn't know that Riri likes him, and partially because he doesn't know if Riri WANTS him to know., and possibly because Eve doesn't know.