Firstly I understand your anger, frustration and fear.
Second.... may take longer. When I was 10 my dad 'gave up his job', he was a director in a big corporation, Mum was a part time 'something' (her career was in radiology but she'd given it up/taken a break because of Dad's job - rightly so, from a 'pot o money' point of view) it came out of the blue for us kids (again rightly so, why heap worry on us) but I suspect that after months and months of my Dad stressing and (badly) vocalising his Distress, suddenly Dad was unemployed.
My dad is a good man, who reached his limit FAR before he handed in his notice.
Anyway. Mum gave him a month to 'de-stress' and he did the garden, and played darts, went fishing and was utterly miserable.
He then got another job.
Here's the relevant stuff. Mum really DID allow him (what she called) Healing Time. He's a good man, a provider, he loved us kids (still does) but he'd reached his limit. He needed his healing time (Mum refers to it as moping time, he did fuck all around the house during this time which must have really pissed my mum off...)
End of story - he eventually got another job. We as a family moved 250miles from home (I was 15, not to be recommended) and started over. It was difficult, major sacrifices had to be made, my mother's frustrations and worries were completely valid BUT... looking back, we all acknowledge that although it was shit for all of us, my Dad simply would not be here now if he hadn't walked. He's a Yorkshireman, proud, strong, a fervent provider, a work addict (so long as the family are ok) and if he walked, we have to trust that it really was a make or break situation.
Your DH has left his job, and that's not easy. Not if you have any pride. You're right to take the stance that this isn't acceptable, BUT... you're a couple, and sometimes you have to soak up the shit of the other and life doesn't work to order. Telling him you're pissed off every time you see him adds no value, nagging him to get work adds none either. If you can mange for a couple of months, then dig deep and manage. He will also not turn into a perfect housewife overnight, especially give the circumstances.
Roll with it. Live to necessity only. If you have no children, and you do have an old horse, what is it that makes you not be able to manage? Outgoings? Slash them. If you cannot survive on just your wage AND keep the horse/child (I mean that respectfully, your horse is important and you can't just get rid) then you need to show your DH the facts... move home, somewhere smaller, somewhere that can be supported on just your wage alone, somewhere that he has no say until he earns.
YANBU in your worry. YABU to think he should just put up and shut up. Shit happens. Believe me it happens big. May as well accept it.