I have had plenty of friends who smoked pot and never drank James so I don't think it's impossible, but I'm not sure these people were ever big drinkers. I've always been a big drinker and avoided drugs because 'I have enough problems with alcohol'. I know as well that being sober has totally changed my mindset...I can't believe how much drinking actually distorted my thinking...I'd imagine pot would do the same thing. Not to sound all after school special but it does sound like smoking pot was a precursor to your alcohol abuse. Is it possible you can't say no to alcohol because you're still smoking pot? It might be worth an experiment...give it all up and see if that helps with the booze.
I hope you find the help you need x
And welcome to SR
x