You don't have to pretend everything is getting better. Frankly, I am surprised that you are.
Why would you ever
think that was a good idea?
It's been 3 years. You said you've been to counseling. Then go back there, either together or by yourself. Vent and get this poison out of you before the stress puts you in an early grave.
Will you stay together? I have no idea. But the way you are living right now-- all three of you-- is toxic and can't be sustained.
You are sacrificing your happiness and your health (even if you don't feel anything right now, stress is a killer). She is probably waiting for the other shoe to drop with you. That's not a great way for her to live, either.
And your son? He picks up on way more than you think. He's well aware that things are frosty between you, even if you think you're hiding it well.
And what's the lesson he's getting from your marriage?
It's that love and happiness don't matter, in the face of the almighty children. And he's learning that expressing real emotions gets you nothing but trouble. He's also learning that stress is a constant companion.
Life doesn't have to be this way for you, and it doesn't have to turn out that way for him.
Go back to counseling and start releasing this anger and resentment before they consume you.