I totally have felt those feelings too. I totally know the feeling of just needing to vent and not have people attack your choices when you try to do that. Sometimes life DOES feel like it's conspiring against you, and I know that my kids certainly pick up on that as well. It's like not only is everything just awful, but then you aren't even allowed to FEEL awful because the kids pick up on it, and everyone jumps in and says everything is awful because you aren't doing enough, or are doing to much, or the right thing, or even THINKING the right way.
I really hope getting a car works out for you, that sounds like it will certainly help you.
I've lived a depressed spouse, and I've BEEN the depressed spouse, and it is SO. FREAKING. HARD. It just is, and I admire your strength and courage.
There are a few things that have helped me, I found out I am borderline anemic, and have low vitamin D levels, so supplementing that have helped as well. I changed my diet, for me low carb, high protein has helped me a lot.
I went to visit my mom for two weeks, and got a break WITH the kids, sounds like if you get your car you have a little help and a break as well.
I stopped trying to find friends/support/help in real life. I'm a huge introvert and it was just stressing me out. Everyone seems so quick to suggest it, but it doesn't necessarily work for everyone.
I stopped expecting DH to pull his own weight around the house or with the kids. I figured I could leave, and be a single mom and have to find a way to earn an income, or I could just kind of pretend I was a single mom, but keep my best friend and his financial contributions. I will admit, after a while he started just doing little things around the house, or even offered to walk the girls to the park so I could stay home and read. I made that mental shift maybe a year ago, and just within the last few months it seems like he is finally getting his depression under control. Not easy, but somehow just changing my expectations changed things.
It's not easy, and I just wanted to say you are not the only one who feels like it's impossible.