I forget I have a brother sometimes even though he lives 5 minutes up the road and we have a good relationship.
I have really poor object permanence perception and as soon as I can no longer see someone or something it's like they stop existing.
He's going through a bit of a mental health crisis at the moment, so there's been a lot of pressure on everybody in the family to keep an eye on him, but I just forget that he exists. When he's here and present of course I am fully invested in his health and wellbeing and I love him but it's just like as soon as he walks out of the door I forget that I should call him or I should text him or just generally keep in touch with him, and it's only when other people bring him up that this mental checklist pops up that is soon forgotten when other things arise.
The same thing happens with friends to be honest. The friends I've managed to keep hold of are thankfully very understanding and proactive communicators but if they stopped calling or texting or popping round it could be months, or even years before they come back into my head.
I am autistic, have ADHD and dyspraxia diagnosed and I don't know if that has something to do with it, but I also know for a fact I have face blindness too.