I think it goes like this.
Ristu liked Itsuki as a kid, and in the first chapter when they were wishing on the first day of snow, Ristu wished that Itsuki was a girl. I'm hoping it was only because he thought he might have a better chance of Itsuki liking him back if he(Itsuki) was a girl (and not a slight homophobic reason). Anyways, back in America Ristu decided it doesn't matter if Itsuki was a boy and wants to reconnect/confess. I'm also assuming he is bi or this is a very awkward love story..