I agree, take some breaks yourself. It helps to get perspective on the fact that at this point in your life there is nothing you can do except what you are doing and you just gotta keep doing it calmly and nicely and patiently and it will definitely get better but you will have to repeat yourself for a long long time. I read somewhere that children don't fully develop the wherewithal to put their self control into play until they are like, 11. So you have a button, and you're like, don't push that button dear, and the poor kid is gonna have a really hard time not pushing that button until almost puberty. It's up to us to not kill them or ourselves, that's all. and the best way to keep perspective on that is yes, breaks breaks breaks. Anything that will keep him occupied for a little while, you take some deep breaths. I participated in a research project through the U of O called "Early Steps" and it was basically a study on stress and parenting, and they give you this huge amount of paperwork to fill out, and every question is a behavior kids this age normally have, and how we respond as parents. LIke, talking back, how bad does it stress you out, not cleaning up toys, how bad, etc. etc. What it taught me is to not take things personally, every thing my kid does other kids do too. It's nothing against me, and the people who make me feel bad for my kid doing these bad behaviours are assholes who never had kids and probably shouldn't.
My kid was the worst 4-5 year old ever. and I have a friend who's 4 year old is worse than mine. It's crazy to see it in retrospect because I just want to hug her and say "it's ok, it will pass" My kids great now. He's a perfect angel. Just had to get through that stage.
They've gotta know they can push you and you'll stay. That's how they grow. I liken it to a rope, hanging from the clouds. They need to climb that rope, to get to where they need to go. So they start by tugging on it. If it gives, they don't climb. If they tug and tug and it doesn't give, then they feel confident to climb. At around 4, they're using every trick in the book to make that rope give. Make it stay mama. Make it stay. Good luck, lol.