hi katie-
just some feedback. i feel your behaviorwas totally merited and appropriate. it is not appropriate to get loaded with your friend's boyfriend. that is not how friends behave.
the issue here is not what he or she do, it is what you are willing to live with...your boundaries. there is no right or wrong really, it's 100% what you want and need in your significant relationship.
your xABF blaming you for his continued drinking is nonsense. all of us have uncomfortable situtations in life, we don't all run and get drunk in order to deal with them. an emotionally mature person would address the issue sober, and hopefully, a compromise could be met.
obviously, this did not happen (except perhaps on your end) and you took steps to sever a toxic relationship with your girlfriend.
reading between the lines, there is the subtle threat that in their drunken, stoned session that they might get together.
i feel you took the right steps to remove yourself from an unacceptable situation, in order to protect your boundaries.
naive