Why do they come back when you’ve moved on?

I was skeptical about this idea but my ex texted me after 3 months saying how sad and empty he feels and thought maybe I missed him and would want to reconcile. Well I do not! Not with what happened and with how he handled everything.

It’s wild. I hadn’t thought of him in weeks and I had felt lighthearted again. Then he pops up. It felt like I was going through the breakup all over again. How selfish of one to do that.