Everyone hating on Tarou. I think the reality for Tarou is much simpler: his first priority is still helping Ririsu get rid of her ability to see first love zombies.
The only way to get rid of Eve is to get together with Ririsu, except he doesn't believe that Ririsu loves him. He believes that Ririsu's only sticking around because she wants to get rid of her ability to see FLZs, and that once her problem is resolved, she'll just go away and leave Eve hanging around overhead. He believes that Ririsu doesn't love him, so being in a relationship with her would only eliminate Eve at the cost of Ririsu's freedom and happiness, and that would not make Ririsu love him any better either.
Tarou is fully aware that Ebino loves him, but getting together with her doesn't solve the problem with Eve. Even if he helps Ririsu get rid of her ability, he'd still see Eve hanging around overhead, and it'd be like cheating on Ebino 24/7. Even if he really loves Ebino, it won't change his first love zombie - his FLZ will always have Eve's form no matter who he ends up with later. And this is true of anyone he ever dates, so no matter who he falls in love with, or who loves him later on, he'll always have Eve hanging around overhead and it'll always be like he's cheating.
So we're back at square one. The only way to not cheat is to get together with Ririsu ... who, as far as he knows, doesn't love him.