Later on, Karl became somewhat attached to me and would spend a lot of time with me. He made a joke that I was his wife and that we should get married and live together, which I took as just that: a joke.
Have you considered that Karl may like/have liked you and is upset because he thinks you don’t return his feelings?
always kind of had internalized homophobia which got worse through the years. Coupled with his anxiety, Liam said it never really felt like Karl was actually into him
This may have made it very hard for Karl to express his feelings without feeling anxious and without hating himself for it. If Liam is openly bi and you haven’t told Karl you like men, he might be more open around Liam for that reason.
What languages do you speak??