I'm glad you found SR, and hope you stick around. As Lexie said, your girlfriend was never in recovery. She may have elected to not drink alcohol, but she still used mood altering substances. That is NOT recovery. As you attest to in your post, you have watched her issues get worse over time. That is the undeniable pattern of addiction, it is a progressive disease.
You seem to take on the blame for her issues. Learn the 3 C's: You didn't Cause her addiction, you can't Cure it, and you can't Control it. You are NOT to blame. What took a "toll" on her is her addiction. Period.
You need to work on your own recovery, and learn about your own co-dependency issues. Read "Codependent No More" by Melody Beattie. You say what you did, you may never do for anyone again. I hope not. Enabling someone's addiction is not love. There is nothing noble in allowing yourself to be dragged down the drain with the addict. Healthy boundaries, and practicing self care, is love. Love for yourself.