@grace49 No shame. When it was first just me and my daughter (dealing with the single parent thing AND the cheating/leaving wife thing) I was at the point, emotionally, where I had written up my resignation letter. Problem was, there was no one to give it to. I felt like I was failing as a dad, failing as an employee, failing as a person and making no headway... every day was just struggle not to drown.
My step-dad told me "I can't believe you're still doing this, I'd have given up" and my honest answer was "If there was a way to give up, I would have."
They're at a tough age. It'll get better as they get easier. This isn't forever, and I know that's not a lot of help, but sometimes that was the mantra that got me through the worst days.
In the meantime...
Cut yourself some slack. are your children dressed and fed and safe? (Or, let's be honest here, some days, just "fed and safe" is enough.) Good, some days that can be all that matters. No one's grading you down if all they've eaten is McDonalds today. So what if all they did was watch TV on the couch? The dishes in the sink can be in the sink. My 3 year old daughter emptied 3 entire boxes of cereal onto her bedroom floor while I was on a critical work call, so we just pulled that door shut, and had a campout on the living room floor until Saturday when I had the mental capacity to deal with 'froot cap'n rice krispy crunch loops' mess. Laugh at the dishes, ignore the sticky floor, ~~pour a glass~~ grab a bottle of wine, take a bath, and breathe.