My heart hurts for my son and now I'm considering getting him into counseling.
I think this is good for several reasons. My kids felt "squished" between parents initially -- their dad would say horrible things about me; they didn't want to tell me because a) they didn't want to hurt my feelings and b) they didn't want any more drama. Having a counselor to talk to about that stuff was really, really helpful to them.
I don't think I'd engage the ex at all. I think I'd talk to the boy and tell him that you would love for him to be with you all the time, but that you've been court ordered to send him to his dad's house. And that it's because the court feels it's important for kids to have access to both their parents. Or that you think it's important for him to have a relationship with his father even though you and his father are divorced. Or something.