Hi LBL,
Even with rehab it is still a roller coaster, there is the drugging behavior (as you are witnessing firsthand), the manipulations, the lies, the deceit, above all the self-centeredness and self-will. These druggie behaviors become addictive in and of themselves. This will take longer to clear his system than the chemicals - much longer, as this mindset becomes a way of life. I hope that in time, E can replace this malignant state of mind with something more positive, maybe NA, which I'm sure he is being exposed to in rehab.
My brother is a crack addict and an alcoholic. Even when clean his obsessiveness is present and he will admit to the self-centeredness which drives his addiction and in my humble opinion all addictive behavior. The only thing that keeps him sane and sober is NA. I can also say that I get pretty crazy if I do not practice the principles in my own life, as far as my codependency and Al-Anon/ACA traits.
Six months is a long time and he is just a short way in. Hopefully you will see real improvement in him very soon. Enjoy your vacation and let E's HP take care of him.