ONG, I can so relate. Even though my kids are older now, it is the same. My SO works 12 hours, then stops for a drink. I end up being along 14 hours a day. Totally gets to you.
For me, I started just doing things I wanted to do on my own. SO, if I want to go to a show, I just go. In your case, you have to get a a baby sitter. If you cannot leave your kids, maybe mediate. I know it sounds like not a lot, but here is a free app for iPhone and the meditations are SHORT, like 5 or 6 minutes.
Maybe that can help a little.