You are putting enormous pressure on him to give you a level of commitment that he does not feel comfortable with yet. That in itself is enough to explain why he pulled back from you.
He's only been out of a significant (3 year!!!) relationship for 4 months. It's not at all unusual that he wants to be cautious when going into a new one ... not because he's hoping to get back with his ex, but he wants to be extra sure that he's making the right choice. It does not surprise me that your demands spooked him.
By taking things in smaller, slower steps (and even him seeking therapy) it will give you both a better chance of having a good relationship in the long run. In the meanwhile, he did offer you a slightly smaller commitment step ... exclusivity. This means he hopes you two will concentrate on exploring a relationship without the distraction of dating others, and expects it to lead a fully committed relationship soon. This is what I think he means by a "slower pace."
His comment "not yet," while somewhat lacking in tact, was completely accurate yet you think it was "dumb" ... I wonder why, embarrassment?
As far as I can see, the only real problem here is your impatience. Why is it so important to you to "close the deal" at the early end of responsible commitment when he needs more time to clear his head? If it were six months, you'd have a point. After only 2 1/2 months, you are still relative strangers getting to know each other.
Carl.