OP sorry to hear you feel like that. I know your children are happy that you exist whether you're still in bed or not.
Life isn't always great, you know logically facebook is fake. Stop beating yourself up comparing lives. If you want a better life then create that life, go back to therapy, force yourself to be kind to yourself. I know that sounds hard to you but your DC don't deserve to grow up without a mum. There isn't a magic pill out there that will give you motivation and energy to be the person you want to be. You have to put the work in for that, but it is doable, you just have to start.
I'd start with,
A chore list for DC.
Going for a walk most days to the park or similar with the DC.
Buy nice food instead of booze.
Look into developing yourself and creating a life ambition. That may be a college course, open uni, learn a trade, whatever you want. Start small with one step and the next thing you'll know you will have achieved a year of working towards something better for yourself.
Have a long hot bath every night. Develop a night time routine so you sleep well and want to get up.
Yoga and meditation. Theres a youtuber called Adrian who does a January start for yoga. Try it.
You don't have to always feel like a failure and feel like shit. You can have the life you want if you create it. Start small. Be kind to yourself. Eat well, sleep well, exercise.