I'm sorry! I think that is a very normal reaction, though. I would feel the same way. As much as you love your son and glad he got some help, that is YOUR T, your special T, and you want his attention. I don't think there is anything wrong with that!
Anyway that you can set up your son with his own T, or even your T, but his own sessions? That way you can both benefit and you don't have to give up any of your time.