I relapsed in feelings for my ex after 5 years of NC

We were together for over for 4 years and broke up over 5 years ago. I went no contact, renewed old friendships, started new hobbies, picked up sports. I was sure I'm a model fucking example of dealing with this. For the last 2 years I barely even remembered her existence.

Our common friend had a birthday a month ago. She invited both of us after making sure we are both ok with this. This was our first contact since breakup. We talked a bit, it was quite nice, nothing crazy.

Last week she texts me that she will be visiting my city and asks if I want to meet her after she's done with her errands. Last time went ok so I agree. We talk for 3 hours, a bit about everyday life, a bit about our past together. We talk about how cool it is to have contact again, maybe we can do some stuff together - as friends of course.

It took me a few hours after this to realize that I'm replaying the meeting in my head, smiling to myself and feel butterflies in my stomach. I'm in love again. I didn't even notice when it happened. 3 fucking hours set me back years of work.