If he is growing that should be an absolute deal breaker and if I were you in your shoes I would feel little remorse about leaving such an individual. Growing pot is not just illegal, and could land him SERIOUS time in a federal hotel, but it illustrates the obsession that he has with the substance and the lengths that he is willing to go to to get it. To me there is no difference between someone who is growing pot in their basement and someone who is cruising around a crack neighborhood at 3am looking for a score.
I also agree with Jenny1232 - every pothead I have ever met has been a total loser. That is why they are doing a drug in the first place - to escape from reality. I am grateful that today I do not have to waste my precious time around people who choose to do any drugs, legal or illegal, on 4/20 or any other day of the year.