Most ADHD people are also susceptible to RSD (Rejection Sensitive Dysphoria(?)) that can make us feel like the entire planet is crumbling when we experience even minor rejections. As in, suicidal ideation level pain that at some point we have to learn how to move through or just avoid relationships altogether.

Must be personal neurochemistry/predisposition. The breaking point hit when my partner showed me a video she took where she called my name 8 times standing right next to me trying to get my attention, and I had no clue. I was so zoned into the screen.

After seeing that I was like damn.

It's not just seeming like you don't care, but also putting the burden on others when they pick up your slack and frequently letting them down by things you do and/or don't do.