How someone behaved in the past is noway a reference point of their behavior today. Irrespective of how little, how insignificant it may seem, everyone learns, everyone grows and so do their mindsets, their behaviors and their perspectives.
Before you judge someone for their past mistakes and behaviors, remove the lens of those experiences and look at them from a fresh perspective. You may be surprised of how greatly the experiences you have, may differ.
Every person you meet after the shortest of gaps, is a different person from what they were yesterday. Meet them with an open mind, be welcoming of their journey and appreciative of their growth... howmuchever little it may seem to you.