Liz, I hear where you are coming from when you say you want to see if he is serious about making changes. I just want to throw out there that your life doesn't have to be put on hold while he works through this (or doesn't, as the case may be). Even if you separated or divorced, there would be nothing really stopping the two of you from reconnecting down the line if his efforts at change are genuine.
And I'm not advocating that. I'm just suggesting that hitching your wagon to his or anyone's else star of change is no way to spend the precious little time we get to spend on this earth. You are an articulate, curious, ever-evolving being seeking answers, and you don't have to depend on anyone else to become the person you want to be.
Good luck to you, Liz -- I am sure there is a sense of relief at knowing for sure what you're dealing with, as harsh as the diagnosis might be. But defining the terms is only part of the process, as you well know. Sending strength and courage your way.