Oh OP, it sounds like you feel so trapped. Quite understandable. Re. Getting help, if someone was running a department (like you) and had too much on, they would hire another person. It's not your job to run this department alone, and feel like a failure or be judged when you can't.
Have you tried having a frank, honest, calm conversation with your DH about how unhappy you are? If not, perhaps give it a go, when you both have some space and time. I don't need to tell you that this whole family game should be a joint one, and the way you win is to all have a happy(ish, at least) existence.
My DH earns more than me, and also works away. I don't love it, I miss him, I feel I often have to take the domestic burden more than I want... But he brings in the money. However, we decided together that we'd have a cleaner, and he always jumps in when I need him to, even if it's just cos I want a weekend day "off".
Is there any chance your older DCs could visit family/friends for a few days, to give you some time to breathe?