We really need to figure out this linking issue with the fediverse. I don't know who is managing the site but it would be nice to be able to produce relative links. For example if OP linked to https://sub.rehab/?follow=kbin.social&separator=m it should be enough to make the links relative to kbin on the page
They need to both start adding referrer parameters to their share links. If hitting share appends /fedirate?follow=kbin.social&separator=m to the link, both lemmy and kbin should be smart enough to replace those values when you view a comment or a post so that it stays on your instance. In the worst case the link still works and the values are just ignored.