Drama is a big part of life...Don't sweat it sounds like a lot of us have been through this. My first summer after my divorce "I freaked" when I lost touch with my son and drove from Florida to Georgia and picked him up. Granted I legally had no right, but my gut instinct was right and my ex and his girl at the time were having some issues and my ex agreed that my DS should go home with me. I am thankful that he's remarried now to a lady I really like because I trust HER more than my ex with my son.
Regardless you have to try to let him see his son because everyones right it could be trouble later. There is no way even the airlines would let him fly. I'm a little surprise your ex would even suggest it. I also agree about the ex mother in law kids are attached to those around them and it would but him in a strange situation.
I must say that is odd to have leave and can't go any where. Please I can't believe it. My ex- served too and I don't ever remember anything like that but that was before 9/11.
Let me also say how that stinks that he's with an old friend of yours. That is messed up. Talk about rbbing the wound some more.
Good luck and you know we're here we got your back