Glad you are ready to get that support, Clear :)
Yes, DS will probably blame you for a split in the short term, because he will still have this mindset which is of course shaped by his experience. His experience to date tells him that Dad wouldn't be annoyed if everyone was perfect and didn't have accidents - this isn't true, as you know, but children are optimistic by nature and tend to believe in the best of their parents, so he will totally believe right now that this is true.
This is one of the painful things that we have to do sometimes as parents. Remember when he was a baby, and you took him for his injections, and he probably cried and wondered why you would let this strange person hurt him. But you did it, not to hurt him, but to protect him. Now he is older he understands about vaccinations and that they are not nice for a short time but in the long term they stop us from getting seriously ill.
So yes, your son will likely be angry, and some of that anger will be directed at you. It is hard to cope with at a time when you are feeling emotionally vulnerable and unsure of yourself to begin with. Please know that it is still the right thing to do. In fact, his anger might even be eye opening to you - a younger child would be upset and confused, but an older one has already learned to blame you, rather than trust you, because when something goes wrong Dad normally blames Mum, and there is some (twisted) logic to the blaming.
Do know that the trust will come back. Short term you use neutral terms to explain the break up by explaining that Mum and Dad find it very difficult to live with each other and are always making each other unhappy and arguing, that it is between adults and sometimes adult relationships break up. That both of you love them very much and that parents do not break up from their children - that no matter what you will always be there for them.
Long term (when he's much older) you can explain to DS that Dad had impossible standards. That you know sometimes it looked like you were winding him up but that you really were trying your hardest to get along and be nice, but still he found things to pick at every day. That such a negative person can be very draining and that ultimately, Dad chose to react in the way that he did.
Medium term, you will see a change in both DC as you model a more accepting environment for them, a calmer one, where people can make mistakes and they get laughed off and fixed, not berated. If they experience the opposite when they visit him, at least it is for a minority of the time, and the contrast with your home environment will also be clearer.