Hello Bikerchick: Welcome to SR. I have not read all the responses to your original post, but I wanted to comment on your last paragraph where you state you are going to stop giving your mother the chance to vent to you.
This realization is HUGE. I remember when I was deep into my enabling (AKA being the victim of an addict), I would call my friends and vent all the gory details. Because I got all that off my chest, when I hung up I was somehow freed up to go back into the situation and get in the muck and mire of the drama of another's addiction. What I found when I quit calling my friends for venting was that the negative emotions would build up inside me which caused me to hit my own bottom quicker. Something I would do when I was calling my friends like that was to focus on what they said back to me that I did not like and use that as justification that my situation was not "that bad."
You are absolutely doing the right thing here. But it does take a lot of courage. Please continue here at SR and Alanon and/or Naranon meetings - not just for a little while but for a long time. This problem did not happen over a short period of time, and it will not go away in a short period of time.