Kayleb's Mommy,
Your work IS NOT down the drain. The symptoms are back because of stress, but all the coping skills he has been learning are still in there. They are going to help him deal with life.
First, I hope you are DOCUMENTING EVERYTHING IN AS MUCH DETAIL AS POSSIBLE. Keep a back up copy of all your documentation. If and when you get a new judge present the whole story from start to finish to him/her. Keep working via the internet and any other means you can find, to find advocates for children and people who have successfully overcome situations such as this. I personally don't know how to navigate the system successfully, but I guarantee you there are people out there who do know. Keep pushing and educating yourself until you find those people. Don't give up. Don't give up.
Tell him not to worry about being told to lie to you. Tell him he doesn't have to argue with his dad about the lying, that he can just be quiet at his dad's and then tell you the truth when he gets home. I think 7 is old enough to understand, "Your dad is ashamed of what he did, and he wants to hide it. That's why he tells you it's all in your head. People always want to hide it when they are ashamed of what they did." Or something similar.
I think martial arts are a good idea, but be sure that you get lots of personal recommendations from parents and kids before deciding on a dojo. I wouldn't recommend it for the physical self-defense against an adult per se --- even a trained 7 year old can't defend themselves against a grown man --- but for the mental self-defense. Also, usually martial arts dojos are full of good men that can be positive role models about being both strong and honorable. As you get to know the instructors and black belts, you will find one or two you can confide in about what your son is going through. But, because I am inherently suspicious, I say don't ever drop your guard and let him be alone with any adult men like this, always go to class and to tournaments with him. You can't risk somebody else victimizing him.
My husband and three sons are all black belts, and it is very good for training body, mind, and spirit. None of my guys are ADHD, but many of their classmates were, and the intense mental training does strengthen their ability to focus. After a year or so of martial arts, many times you can't tell who is diagnosed ADHD and who is not.
Eventually, as your son gets into his teens, martial arts training WILL enable him to say no to the abuse (assuming you have not found a way to get him out of this absurd visitation by then).
I sound really bossy, don't I? I don't mean to be ... I am assuming that you will feel absolutely no obligation to do anything I've suggested if you find it wrong. I have had several cups of coffee this morning, I think it revs me up.