User blog comment:B214/Volume 22 spoilers/@comment-28087053-20161103132931/@comment-24941352-20161104201235

VongolaGitai the answer is simple, Irina is in love with Issei since their childhood so i don´t think she would fool around with a other guy. She is pure and naive like the other members of the church trio. And i t´s unusual in the anime/manga world that childhood friends don´t become a couple or one dates a other person first.

Ah B214 reveals the story already :D