That’s part of autism. I’ve dealt with autistic adults and having a fixation is a symptom. One was into photography, one was a foreign army buff, all kinds of stuff. I helped with mood stuff but actual autism treatment is behavioral therapy. Exposure and literal teaching by coaching through practice. The frustrating part is like no matter how much you teach there are some situations that can’t be chanced. He’ll probably get that and a lot of other things late, but he’ll get it eventually.
Never leave him. He’s high functioning. I’ve seen people like that but have no family or family that isn’t involved. Their fate is group homes that send them to adult daycare centers during the day. Sad lonely and depressing. Group home gets all of ssi check and they are rationed out like 60-100 bucks throughout the month which usually supports their cig habit.