Parenting in the midst of a marital crisis is the hardest thing I have ever done. You sound like you are doing a fantastic job. I have a son same age as yours and am dealing with some anger and outbursts that make me so angry at H and how his decisions are adding to an already-full plate of pre-adolescent emotions in our son. But, like you, I have to put that anger aside and put on my best face (which isn't always possible), plug into my higher self and be the best, wisest mom I can. Day after day after exhausting day. Family to lean on is a godsend, we both are so lucky to have that.
Growing up, there was a trio of amazing, well-adjusted kids that were raised by a single mom. The kids were popular and kind and smart and everyone loved them, peers and adults. When I am at my worst, I think of that family, and how hard it must have been at times for the mom, and what a great job she did with her kids. That it is possible. To raise such great humans. I'm sure the mom wasn't perfect, I am sure she had her days, but it was probably just those small, singular acts of courage, patience and wisdom that made those kids the way they were.