Just fed up

I have a fiance and 3 kids all under age 3.... Fiance is never home I'm a SAHM i cook, clean, take care of the kids (we have a special needs and a heart defect kiddo) so i deal with all the specialists, appointments, doctors, teachers for special education, he works yet I've been the only one finding ways to make up for christmas (which isnt really anything) my kids never sleep so i get 1 to 2 hrs of sleep everyday, i HATE his family because they are all parent wanna bes and judgemental jerks. Nobody wants to watch my kids and give me a break so I'm with them 24/7. I feel like I'm slowly breaking mentally emotionally and physically. I feel like I'm failing as a parent, i feel overwhelmed and over stressed. I've battled with ptsd and depression, sometimes i feel like release is so close all i have to do is go away for good but the only thing that saves me is my girls i can't leave them alone to fend for themselves. They need their mom. My relationship with my fiance is pretty much non existent and i secretly am starting to hate him for always being gone and acting like nothing is wrong and me shouldering all this weight.