My ex called me before he got married and apologized for never actually sleeping with me. (He's Mormon)
my husband left his ex fiance for me and when we got married he got coffee with her to explain why and didn't tell me!!!
When I was almost engaged and my ex had also moved on, he call me and apologize for how he treated me and hoped to get together sometime for lunch.
I apologized to an ex for leaving him to be with my now husband and my husband got extremely pissed off
I made my hubby apologize to his ex before we got married. I think its made our relationship more open and understanding.