Does anyone else ever get obsessed with someone and then later end up feeling completely indifferent towards them?

I was in a rut earlier this week and then I randomly started thinking about my ex and what it would be like if I got better (fixed up my appearance so I was more comfortable in my skin, worked on my mental health, etc.), so we could actually become friends. I was so enamored with the idea I couldn’t stop think about it, and it made me feel alive again. 

However, I’ve now come to the conclusion that he’s just a terrible person and feel nothing for him and just feel like shit and empty. I’m not at all angry, just sad, because I feel like I can get so obsessed with a person or identity and then just lose interest it in it like it meant nothing to me.