When I read your post birky, what stood out to me is how your son wanted to talk about a challenging relationship issue he was having with a friend. That was something important to "him" and next thing the conversation was about you and your husband. IMHO, all of the adults "failed" in that meeting because your son did not get to talk about something very important to him.

Your arguments with your husband has contributed to your son's stress levels. HOWEVER, at his age he is trying very hard to navigate the challenges he is facing with his piers. Right now, at his age that is what is important to him. But the conversations he has tend to focus on you and your husband instead of HIM. Yes, your relationship issues are "part" of the problem, yet, that's just back ground to him, he is focusing on himself right now and his friends, THAT is where he needs help and guidance.

He needs someone that can mentor him in "how to relate" in healthy ways, and it sounds like he doesn't see that take place in his home life. He is lost right now and the therapist is making it about you when he REALLY needs it to be about him.