Mrs. H, It's not that you went wrong. Your h has a lot of resolved issues from his childhood and life tossed him some triggers that triggered the re-evaluation of his life. I honestly don't believe that there would have been anything you could have done differently that would have changed the course of his life's journey. If he had not hooked up with the young ow, he would have hooked up with someone else. Unfortunately, they just never grew up and we grew up a long time ago. They are on a mission to find themselves and no matter what, many of them leave a trail of destruction behind.
I'm so sorry you are feeling down and miss life as it once was. It's very difficult, especially with two small children. No one wants to be here and none of has deserved what they've been dishing out to us. I truly believe that most of the marriages/relationships here could have been saved had the spouses been rational and communicated w/us. We are not mind readers, nor do we have crystal balls that can predict what will happen. It's very unfortunate how they deal w/life. Everything could have been done differently, i.e., a more mature and rational way.
I wish that I could give you a hug.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.