I believe that Kei is a non-binary person, well, it looks like he is fine with any pronoun, but he is not a boy and neither does he consider himself a girl. I don't believe the description "boy who dresses like a girl" applies to this story
It's a bit confusing because the author doesn't help much and i sincerely hope that the manga explores the ideas of gender and sexuality, but i don't know if that will happen...
Um, well, the BL manga "Boy Meets Maria" explores the idea of a non-binary character more naturally...