I still haven't watched the episode yet, but I've read a lot of discussions on this and I had some thoughts on Kody responding to this in general.
A normal person would be feeling a great deal of regret, shame, and grief right now. I'm not convinced that Kody is.
I don't know him. I haven't met him. I've just seen how he conducted himself over 19 seasons that spanned 14 years so far. He's shown that he's motivated by his ego, how he feels about himself, how others view him, and how others make him feel.
A normal person would have worked overtime to fix his relationships with his remaining children in the wake of this tragedy. Based on interviews with Janelle and Christine, as well as what Mykelti has said on her Patreon, he hasn't done that.
Why? It's simple: Kody doesn't want to feel bad about himself, feel that he made mistakes, and he certainly doesn't want to feel like a failure. So, he surrounded himself with those who don't make him feel like a failure but a hero. That used to be Meri, Janelle, Christine, and their children. Over the years, that changed. Meri became unpleasant to be around. Christine was constantly highlighting his shortcomings. His adult children see what a failure and what a loser he is. Janelle sided with their children over him. The Tenders are still trained to idealize him,so he rewards the ego boost.
This isn't about Kody’s romantic partner. This is about him, his choices, and his behavior. I think it's much more complicated than "X arrived, and everything changed!" It's about what motivates Kody as a person and how fragile he is emotionally. He's literally reliant on those around him boosting him up. Rather than working for quality relationships, he sticks to the ones that will take the least effort and have the least risk of hurting his ego.