Yes, I think you have hit the nail on the head re. not really being in touch with reality any more.
This is so far from normal.
It's heartbreaking to see you live like this, subject your children to this (it's not normal or good for them to see this relationship played out in front of them, or to have their understanding of a father figure as someone who just disappears for ten weeks, or for you to know you just couldn't be so cruel to them as to leave them in his care for more than a short period) - all because you have in your head some mirage of a 'good man' you once knew.
Let me tell you - that man never existed. Good people don't just turn into selfish, aggressive, nasty characters just over time. No, what happens is that when you don't have children, a man with a partner like you - someone kind, unassuming, caring - can do a good impression of a normal, caring person themselves because nothing is ever really asked of them. It's when the chips are down you see what someone is made of. This guy is made of shit.
It's about more than practicalities. You NEED to leave this scumbag because right now you are being ground down emotionally to the point where you and your kids are suffering. I promise you, any extra stuff you have to do will feel like nothing - because you will be free of feeling like this, feeling like you are being spat in the face constantly simply by him being there watching you slave and stress while he chooses to 'relax'. You can stop feeling like that, you can become instead the presence your kids need - someone who laughs, who is super busy but ultimately the master of her own destiny.
I've nothing to say about him, he'll probably contribute nothing because he IS nothing. Emotionally, it will be a net gain for the children because right now they see him abusing you, and they are absorbing that message - this is how a mum is treated. This is how 'people who love each other' are . This is what a parenting team looks like. Get out before your son becomes a lazy abusive teenager or your daughter gravitates to men who act like abusive boors.
Re work. If you have a disproportionately heavy workload, can you raise this? Ask for a meeting to discuss your working pattern and if there are obvious potential changes (are you doing a LOT more than others? Could some classes you have be shared?) be upfront - you don't want to burn out, here's a solution, can things be tweaked?