One thing at a time mate. Maybe reducing the debt, which might take some hard choices like cutting back on holidays (at least, not spending so much on them) or things like alcohol/cigarettes (which will help in itself (no idea if you drink or smoke). Getting your monthly payments down will make work easier and after some time you'll have money for yourself.
That's where I'd start, personally, but that's me. Addiction - seek help from your GP, just be open with them. There's all sorts of counselling groups.
These are the two things that you can take control of, don't stress about things you can't control. It seems unfair, but stressing about it changes nothing.
Appreciate your current partner (I'm sure you do) and make sure she knows that. Enjoy the good moments when they come, even the little things. Every good moment is a win.
Lastly, remember your nana would want you to be happy. Used that memory as motivation when it all seems pointless. Your nana, your partner and for the times that you can see your kids.
Take care mate.