Thanks so much for all the advice everyone. Just to answer a common question, the reason she doesn't like it is because it is illegal and she thinks it will ruin my life. Where I live, if you are caught with up to 50g of pot you may get a fine or warning but it is not a criminal offence and you will not go to court. I never grow over 50g and never sell so I'm pretty much safe. I also never smoke unless I have the next day off work.
I took all your advice on board and told her that I choose to smoke weed and thats final. I explained all the reasons why it's not a big deal but it's like she is brain washed she won't listen. Anyway right when I thought we were about to break up she caved in and said that I could do what I want and she trusts me to not let it take over my life! I am stoked, now I get to keep my girl and I can keep smoking

I just hope it lasts and she doesn't go back on her word...