I feel for you. I really do. But the thing is, surely you knew all this before you married him??
I am not being unsympathetic at all, quite the opposite. The thing is, my DH. I knew before I married him that he was academically less able than me. He just doesn't have a brain for understanding finances (or at least not to a level where he could look at our bank balance, look at the money due to come in/go out, decide if we will be ok, and factor in incidental expenses, etc). He could do it, but it would take him a long time, by which time it would all be different.
He is not a quick decision maker, and as a result would make rash decisions on impulse rather than prompt but careful decisions.
He means really well, and will do lots of household jobs willingly. But he doesn't multi-task information well. He will put on a load of washing, but he will put on the type that there is most of, rather than thinking of whether there is a particular thing that is needed, i.e. uniform for the girls.
But I knew all of that before I married him, and there is plenty about me that needs changing too.
I don't think you want to leave him. I think you want to be less stressed.
Do SS help? Are they aware of your DH's SN? You may find that you get more help if you are designated as his 'carer' as well as your DCs.
I know how it feels to feel that you are responsible for all major decisions and day to day responsibilities. I don't think leaving the man you love is the way forward though 