Helene,
You did the right thing. Sounds like (to me) that there were other issues at hand than the pot smoking---that was just another straw. DOC's like cocaine and opiates are different in the fact that they change the receptors in your brain (see my previous posts for a detailed description), and in that respect are much much harder addiction to break. Alcohol is a whole 'nother ball of wax that for it to create dependency depends on the person and their genetic make-up. To stop smoking pot usually just results in a slight headache and maybe a bit of irritability the same way that stopping caffeine does. The main thing about pot smoking, when one is using like your ex was is, that it does exactly what you found irritating: it creates lethargy, unwillingness to work, lack of motiviation, etc. I think that is the main problem. It is hard to move forward with life when one is wrapped in a haze.