True fact. I never understood until my arse of a 'DH' left. Just disappeared, and told the children immediately that he was 'never coming back'.
We were always sickeningly happy (so I thought), rarely argued, and often discussed how amazing we were together.
In retrospect, he'd always told me that he had walked away from very serious relationships, without much of a second thought.
One was an engagement. 5 weeks away from huge wedding. Argument about something ridiculous. He just walked out.
He said she was 'crazy', and gave her an appropriate nickname. His children (no kids from that relationship), used the same nickname for her. 
She'd apparently had a breakdown following the
break up. Suicidal behaviour, etc.
I wonder why, poor woman.
It didn't sit easy with me, but I thought that we were different. 

He told me who he was. He married me, then fucked off after I called him out on a lie. He gaslighted for a while, then went into 'poor me' mode. I made it clear that I was unwilling to accept lies, and tried to make him understand why I was angry.
I was committed to making it work, but I needed the issue to be addressed, discussed and resolved. He tried to brush it under the carpet with declarations of love. I needed more than that, and made it clear.
So he dropped off our DC at my parents', and fucked off. The end.
It broke me for a long time, until I realized that I was just a tile in a huge mosaic.
It broke the children, and I will never forgive him for that.
My DP is a gem. I grilled him on his relationship history, and he's just pragmatic about his past. No name calling, or twattery. 