Apart from your problems at work, what pressures are you under that do not also beset your dh?
Why would your dh 'freak' if you explained to him all of the pressures you are under?
If you are referring to the pressures brought about by your inner thoughts, has it occurred to you that your dh may be feeling much the same as yourself? Or do you believe that he has a more efficient coping mechanism and/or is more equipped to soldier on through times of great stress without internalising his thoughts or allowing them to unduly impede his performance?
Has your ds been discharged from hospital and, if so, is he back at school? If not, how will you care for him if you and your dh are working full-time and is unable to return to school immediately?
How do you manage ds's care during school holidays and does he still spend one night a week at his school during holiday periods?
Can you not use this one night a week's respite to catch up with your dh - perhaps make this time sacrosanct so that you both have opportunity to reconnect with each other, recharge your batteries, and make plans for the forthcoming week and longer term where necessary?
It seems to me that, unless you are able to raise your game, it could be that you may not have the option of continuing to work for your present employers much longer.
Looking at the household budget, given the benefits you should be receiving on account of ds's disabilities, is your wage absolutely necessary?
Would it make more sense taxwise and otherwise for you to consider looking for part-time employment or, indeed, giving up work to continue your studies and be on hand for dmil thus relieving your dh of some of the burden he shoulders in regard to her welfare?
Or would it be financially viable for your dh to go part-time or give up work so that you can concentrate on your career and further your studies?
You've mentioned that your dh's siblings have expressed themselves as being willing to do their bit. As they are not located close enough to be hands on, it would seem that any contribution they make to their dm's welfare should be monetary which will enable any services needed to maintain her in her own home to be bought in. In addition, your dm may be entitled to attendance and carer's allowances which may also help to relieve any financial strain caused by meeting her needs.
Resolving the practical issues that are keeping you in a perpetual state of Groundhog Day may be the first step to you regaining some sense of positivity about the future, but if you decide that you should give up working full-time you're best advised to do so in a spirit of affirmation that this is in your best interests and that closing that particular door will lead to new doors opening for you, rather than seeing it as yet another sacrifice in a long line of many that you have been required to make over the past 10 or 11 years.
FWIW we all have our own personal gods and devils, but the Imps of Shit are common to all of us and they rarely miss an opportunity to chuck another bucketful down whenever they notice a head surfacing above the manure.
The only way we can dodge the onslaught is to shelter beneath an umbrella of certainty that we possess the shovels that will dig us out of the piles of crap that rain down on us.
But you know something, honey? It is possible to be at peace with oneself in the face of adversity and it doesn't have to be a struggle unless we choose to make it so.