Hi Nicki.  I have a 3 year old and understand how you feel.  Except in my situation I am dealing with the constant No's, and him trying to test me in everything we do.  I think in your case, he might be scared that you won't come back, in other words, like he got lost and is alone.  Did anything ever happen like this, like him getting lost in a store.  Or maybe he got scared of something and it is triggering this type of meltodown when you are not present.  I know many kids handle situations differently, also depending on their personality.  What I would do in your case is try to explain to him (although I understand you are dealing with a 2yr old) in the best possible way that you will be right back, and if he needs you he can find you right away.  He might just be looking for the stable feeling of knowing you are there. Maybe preparing him and explaining will ease his tension.  Hope this helps.

Vicki
www.luxurylittles.com