My ex from 4 years ago recently started contacting me asking for another chance. We lived together 3.5 years and when he didn't want to get married, I kicked him out. WE WERE NO CONTACT FROM THE DAY HE LEFT!!!
I am no longer interested in him because of some shady things he did back then but I could marry him tomorrow because he is so hung up on it. I think truly thought the grass was greener and went out in the world, dated, and it was not what he thought.
But on the otherhand, I have had a few ex's I never heard from again. My friend and I believe, if you treat your partner real good, at some point, usually when you really don't care at all anymore, they pop up. Not sure why that is...the universe of push-pull, I guess.
It can happen. I think my motto these days after breakup is, move on but never give up hope. You could reunite with a loved one 20 years from now. You never know.