I joined the workforce in the early 1990s and while I've had plenty of busy jobs, employer expectations have definitely worsened and become beyond unrealistic in the last ten years or so. When I was first in the workplace companies would get a temp in to cover holiday and sickness and mat leave. Not any more, or very rarely now, the rest of the team just has to suck it up as far as employers are concerned.
Burnout and work overload and expecting everyone to be able to do the job of three or four people just seems to be an expectation now. It's not sustainable, and so few employers care these days.
Your first responsibility is to yourself, and things don't have to be perfect, just good enough. And no matter how good you are, you're still only one person. The most brilliant person on the planet still only has 24 hours a day to use, even if some batty, ungrateful and downright abusive employers do think we should all be spending all 24 of those hours devotedly beavering away for them... we're not robots but too many employers seem to think we should be.
I'm presuming you've kept a written record, preferably emails you've sent, of every time you've raised this with your boss? If not, you really need to, so that you can point out, with proof, every occasion when you raised this as an issue and no mitigating action was taken, in fact your boss made it worse by piling more work on you (I'm hazarding a guess here that they've never done your job so have no clue whatsoever how long things take).
Also, what's your company bullying and harassment procedure? Are you at the stage where you're thinking it's a grievance? Do you have an occupational health team? Health and safety, duty of care - failing to safeguard these can prove very costly for organisations. Can you see your GP and ask to be signed off for stress? And are you in a union?
I've been where you are and it made me very ill, to the extent I had to drop out of the workforce for a couple of years. I'm much less invested in my career now, it's just a job. I'll never be that senior or well paid again but I actually don't want to be, it's not worth the hassle.
You only have one life to live, as this you, you deserve to be happy. I hope you find a solution that will work for you.