Does everyone do this? in General feelings on things

It has been years since we went seperate ways but I still have this guy running through my brain. I see him from time to time but I always just say something stupid or ignore him to avoid being awkward. We have both built up completely different lives, but no matter what has happened he is still the first thing on my brain everyday. I don’t initiate contact, I dont talk about him, or creep his profile or anything weird like that. In fact I’ve tried anything and everything just to shut him out and move on. Still he is there. Does everyone do this? Is this a normal thing? Is this an obsession? Am I completely crazy? How do I make it stop?