This. Hotarun did nothing wrong. She has serious abandonment issues because her mother left and her father is gone most of the time working. Yuma was the only person she had and she's already gotten close and then ditched her for other friends once before.
Sure, they were kids and Yuma isn't a terrible person for it or anything, but that's what happened. It's only natural that Hotaru is completely unable to trust that anyone actually loves her or will stay by her side when her entire life has just been the people closest to her leaving, and others looking down on or despising her.