Could be due to long term drug abuse but not sure when he started taking them so I could be wrong
Depression can actually cause memory loss and even hallucinations
I think both replies are right, it's likely both mental health issues and substance abuse
When someone dies, you tend to forget their existence, so that the pain can be forgotten and not run fully insane. It's a very painful experience
I reread some of the early chapters and realised that the mc's memories are really really messed up. When the ml punched him, he was under the impression that his mother was alive then, but it actually happened after his mum died. And after cremating his mother, he forgets her ashes and so much more he's forgetting. I'm so confused, is this some sort of mental condition?