Contact your predecessor or reply after breaking up.

If you are still single, or want to be friends, or really have something to do, you can contact. Both sides had better have this tacit understanding.

But if one party already has the other half, then don't contact.

Unless you want to save this relationship, then contact. But if not, then don't contact, after all, it's really not good to break up with your ex.

Just a personal thought. Don't spray if you don't like it