I don't actually know what possessed me to write this but I think I just needed to put it all somewhere so I could work through Kanji's thought-process myself. It's not terribly well-written but I've been up since 3:00 PM yesterday, so it's good enough for me.
When the relationship started, Kanji really, truly believed he was okay with the fact that Shinjiro was dead and there'd be no chance of them meeting back home. He really thought that it would be enough, for them to only be together at Camp, and that it was okay that Shinjiro was happy being alive, even if it was only in Camp. After all, no one knows when they're going to die, just like no one knows when they're going to leave Camp. So, in Kanji's mind, it was the same thing. And, for a while, it was okay! Then, right around the time their bodyswitch ended and they slept in the same bed for the first time, Kanji, like the derpy idiot he is, fell in love. And then it wasn't okay that Shinjiro wouldn't be around after he left Camp. It wasn't okay that Shinjiro was starting to be happy being alive only for it all to end as soon as he left Camp.
And so, even though he knew it was entirely pointless, Kanji started to wish that it was different. That there was something he could do to make sure Shinjiro would stay alive outside of Camp. When he heard that Yuuko's shop only appeared to people that had wishes, and he couldn't see it, it was like a punch in the gut. Why can't he see the shop? Does he not want it enough? Is he worried about the price? He's sure he'd give up sewing to keep Shinjiro alive, because in his mind, the two things aren't even comparable.
The fact that Shinjiro--grumpy, closed off, emotionally damaged Shinjiro--sticks by him even when Camp does all sorts of things to strain the relationship, like turning Kanji into his Shadow, or growing flowers that make him feel the exact opposite of how he really feels, makes it even worse in Kanji's mind. Shinjiro's doing so much for him, and he feels like there's nothing he can do in return.
Constantly warring with these thoughts is the fact that Naoto--second only to Souji in terms of people Kanji looks up to--is constantly trying to figure a way out of Camp. Kanji really doesn't know what he'd do if Naoto succeeded. He knows that all of his friends would want to leave, and he assumes--hopes--that Shinjiro would want to stay, so that he could remain alive. Kanji honestly isn't sure which he would choose, if he had to.
Even worse is the fact that Kanji knows sometimes people just leave Camp without any notice. The fact that he could wake up one day and Shinjiro could just be gone without a word of goodbye or a single thing left behind is something that he thinks about often. This is all part of why Kanji is so touchy-feely when it comes to Shinjiro (the other part is that Kanji is just a naturally tactile person). If he never lets go of Shinjiro, then Shinjiro can never go anywhere without him. He's determined to not let any of it show to Shinjiro, though, because he's worried that if Shinjiro knew about any of it, he'd end things so that Kanji would stop worrying about him.
So, yes. Things are complicated for Kanji right now.