Seeing a lawyer doesn't "mean you're leaving"--it means you are exploring all of your options so you can make decisions based on facts, not vague fears and speculation. Knowledge is power. Information is ALWAYS helpful. There may be planning you can do right now that will protect you financially, in the event you decide in the future to take that step.
And the fact that he's not "drunk" at any given moment doesn't mean he is thinking rationally. I'm eight years sober, and it took almost a year for my thinking processes to work properly after I quit drinking. While he's in the throes of alcoholism, his primary drive is the drive to drink--and that means everything will go through that filter.