My (39F) coworker (32M) had an extreme attraction and briefly (a few months) dated. Why can’t I stop thinking about him a year later?!

As soon as we met there was an instant almost animalistic attraction, I can’t really explain. We enjoyed working together as well, but I noticed a few red flags (him getting a DUI, ghosting me off and on) so I ended it. We had been texting/snapchatting here and there for over a year until I learned he was seeing someone. I instantly felt sick to my stomach and broke off all contact, but CANNOT stop thinking and obsessing over him. Have I lost my mind?? Why do I feel this way even though I’m the one who ended things?