From what we can read, I think he fears him in some way. I think Kay thinks that Della sees him more of thing he wants because he has use of him like a child when they like some toy, after they don't like it or don't have use for it they throw it away. We can see it in the narration part where he says he is possesive and that's how he percieves their relationship.
They need to communicate more as this is going bad way, Della is sincere about his feeling but he's showing it little not enough or by wrong vibe idk, but Kay also needs to communicate and say what scares him or this will continue him ruining away just for Henry to have in his grasp once agian...
I wanted to come here and say that aww they are communicating and it's finally going green way but came to comments about his d*ck once again and cum on face instead of tears and how chopped the artstyle is. Well I don't want to stand on any side, but guys you are still here which means you must enjoy the story no...? ╮( ̄▽ ̄)╭