I think it's just a friend. She mentioned " whenever I'm near girls I...." which could mean that she prefers hanging around with dude friends because she feels weird/attracted to girls
Probably because his 17 year old self is waaaay more imature than his older self. And seeing Yu Qi showing so much interest for someone else triggered him into action, to steal and to confess. While in the other timeline he didn't feel the need to act sinze Yu Qi didn't show interest in anyone
"Nah, I'm not interested in it"
-brings the whole outdoors sex kit with her just for the chance of it happening
Yeah Yuiko, you are totally not into it.
My bet is that Kan has the gay too, and he finds it extremely unfair that everyone hated him and Miwa get's to be coddled with everything she does.
it's just that Miwa is too damn cute Kan, nobody can help it