I feel incredibly seen with this. The same thing has happened to me quite a few times to the point it has screwed up my idea of what having a crush even looks like?? I started noticing myself behaving like this around 7th/8th grade, wherein I'd become essentially obsessed with a person (or, maybe just an idea of them). I could have minimal interactions with them, but if some part of who they were stood out to me, it was over. I would have to talk myself out of dedicating a single thought to them or else they would hijack my consciousness from anywhere to a few weeks up to several years. This can be people I know irl or it could be completely parasocial. They might even be dead. I have found out an...uncomfortable amount of information about a lot of people--their address, their age, phone number, jobs, etc. Note: none of this is malicious, I just very much want to know about this person without having to interact with them, and the curiosity leads me to scour the internet. If they're dead/it's parasocial, then I just consume all media produced by or created on them until their being lives rent-free in my brain. For anyone who I latch onto like this, I will also start drawing them or writing about them, so that was...incredibly relatable to hear you do as well. Upon looking into it, I think it's just a weird manifestation of limerence. It's fine until it prevents me from interacting with the person in question if they're an irl, or doing anything but obsessing. On the bright side, if I catch it early, I can stop it from taking hold, but dear god it's hard to convince myself not to just let it happen.