Stop attacking Gail and listen to the point. You are a bit dramatic and I'm being kind. You have to understand we see people here all the time in your situation and there is ALWAYS two sides to every story.
I believe you have an issue that needs to be resolved and we are willing to help you. However I also believe that you are a very dramatic person who probably blows every thing out of shape. Here are the things that are LEGAL in nature that you can deal with.
1. If your divorce decree states that he is to give you his address, withhold the child from visits until he gives it to you and it is verified (that is ok).
2. I would also think that you have the right to know the address and phone of his girlfriend IF AND I MEAN IF you will leave them alone. That address and phone number is for EMERGENCY USE ONLY.
3. Having a 5 year old boy and a 7 year old girl sleep in the same bed once in a while is simply not a federal case. (This and some of your other statements is where I get the Dramatic reading from). If the girlfriend's brother was sleeping with her that would be different (assuming he was an adult). Your comment about molestation is a bit over the top if you have no proof whatsoever that she is in danger of molestation.
4. I can tell just from your posting that you are hostile, emotional, and dramatic. It really isn't that bad, chill out. I would bet your next three child support payments that if you had the girlfriend's phone number you would call it repeatedly. If I am wrong and you can act like an adult about the fact your child is spending the night at another woman's house then you should have it.
If you attack him like you did Gail, then you are a good deal of the problem. Don't ask for free advice and then tell us how to give it. If you want to do that, go pay your attorney.
I hope it works out for you, I'm not trying to be mean, you aren't the first or the 100th female I've talked to in this situation. Just keep calm and focus on what IS HAPPENING not what might happen. When he has the child, that's his job.