As a recovered heroin addict and a loved one of addicts, I can tell you that there is nothing more that you can do to help him. He has basically be given numerous opportunities to try all different programs and yet he made the choice not to embrace them.
He isn't going to learn anything new at another rehab, he has already been to enough to learn what rehab teaches. Now he needs to want recovery more than anything, and apply what he has learned.
Have you thought about setting boundaries with your son? It sounds like he knows how to get you wrapped up in his recovery by promising to do this or that, when you know from the past he never follows through with it. He is draining you for every penny you have, if he really decides he wants to get sober, there are plenty of free resources.
Maybe you should take a little vacation to clear your head and just relax. Loving an addict can drain the life out of us, it is important we remember that we are important too.