Any time you feel you should get a therapist is the right time. Also, as hard as it is, your child will survive as long as you and your ex do find a way to co parent with each other. You can reassure him that his daddy loves him, and you can also help him dial his daddy.
No matter how your ex acts at least you be calm and civil. That way your son knows he has at least one person he can count on.
I suggest reading
The Divorce Buddy System , you can see a review I wrote on it on the main divorce page