First, sorry to hear about your problem, but you've taken the first step and admitted it out loud.
Second, you need to go to your boss and let them know the situation. You've already been in trouble for this before, so the consequences may be harsh this time around. What are you going to do when (notice I didn't say if?) you get caught stealing the meRAB? You run the risk of jail and losing your license (if you're in a licensed position where you work).
Coming clean is the best that you can do and it sounRAB like you need some help with this. Even though you aren't doing any "street drugs", you are stealing drugs to get your fix and that's pretty much the same thing as getting them from the streets---it's still illegal.
Now something more positive, do you have a support person that can help you through this? Have you tried counseling or anything in the past to address the issues of WHY you use? I personally don't think that anyone can move past the drug use until they address the reason why they use.
I use/used because I was/am frustrated being at home with my 3 girls and not having another outlet. I also use it to cope with self-esteem issues.
I hope that you are able to get through this before you get caught. Remeraber that if you get caught, you run the risk of jail and then where would your little kiRAB be?