I disagree with the doctor. When I was in court, I had a psychologist state that children really dont notice the change as its magic, the court appointed doctor stated I would harm her and that he could "cure" me (his son, gay BTW, committed suicide a few months later).
Be involved in your sons life, talk to him. Staying away as the doctor says, is hiding, it may make him feel him that you are embarrassed, that some thing is dirty or wrong about who you are and what you are doing.
Let him see you as you are, getting up every day and facing the world. Going to work, inteacting with people. Let him see you overcome obsticals and let him share in your successes. Lead by example.
I understand why you sat in the car waiting for the people to leave. It hurts and it sucks, but I also applaude you for it. Your ex has her own life and it was nice of you to sit back for a while while they left.
Use Skype as the above poster stated. Great idea!
Good luck and stay strong.