It's really easy to get a bad end for Kahl, but his character specific bad end is the protag isolating yall somewhere and kahl obsessively devoting his heart, soul, and body to them (with no interest of leaving). You can also get a blanket bad end where the protag says too many things wrong and Kahl won't speak to you ever again. It's kind of hard to get a good end for Kahl, because it requires you to not give him what he asks for, and instead what he needs. Which means sometimes the right answer is to tell him no.