I agree with other posters.

It didn't sound like a relationship at all. It's not even that it was weird or he was weird, it just wasn't a relationship. That's why he probably didn't bother explaining anything.

I'd focus on the fact that in three years you didn't figure out that it wasn't a relationship. And whatever that was ( simply sex or just hanging out etc) clearly has been over for two months and it's no point to keep investigating why.

Perhaps I'd see a therapist eventually trying to understand my own perception of things (not why he this or that).

Good luck