Had sex with my manager...

I few years back I worked @ a retail store as a supervisor. I went through a tough break up and slept with the gm of our store. He was separated, and I was getting over my break up. Fwb kind of thing that lasted a few months. 6 maybe? Work was amazing, we had an awesome relationship, and things were never awkward. Even when he went back to his wife we were friends. Fast forward a few years, I'm engaged & getting married in 3 weeks (yay) and recently ran into him at the grocery store, and I CANNOT stop thinking about him. Not the sex. Him. We have always been friends and what not, so running into him at the store was cool. We hugged, caught up, and it was good seeing him. He texted me a couple of days later just to say it was good to catch up, and that was all...but I seriously cannot stop thinking about him. I love my fiancé, but is this normal? I feel completely awful for it, but it's a feeling I just can't shake. What do I do?