@Loksel
This kiss was him retroactively and reactively reciprocating Ibusuki's love, so if Eve was a normal Zombie she would have disappeared.
It seems to me that he's living out the memory as a firsthand experience. When he says "Even though I love Eve this much", I think he means Ibusuki. Not Eve, not little girl Eve, but present Ibusuki.
It's safe to say that he won't forget the promise now, unless Ebino is waiting around with a bunch of softballs to lob at his head. ???
Sigh... I really hope that this doesn't mean Tarou will end up with ibusubitch. After all the lying and crossdressing and getting angry because tarou didn't shower her with love even tho she was supposed to be a boy I really don't want her to win.