The only ONLY thing you can do is rise above it. It sounds like he is acting like a child. He is dating a child, too! You are both pretty young, relatively... had your kids pretty young. He is just not quite ready to be a grownup. But your boys need more than that. YOU have to be the grownup. They need someone showing them what it looks like to put someone else's needs (theirs) above your own.
Work on yourself.
Stop doing so much thinking about what he is or isn't doing. You can't change or control him. Have you found any resources (book, support group, etc) for dealing with a difficult ex as a co-parent? You need that. Your L is not the best resource for that in terms of how to best help your sons emotionally.
Hang in there. But let go of some of your anger and frustration towards him so that you can become the best YOU possible.
