I think that was a major step for you making and keeping that appointment! It sounds like you got some great communication tools to use to help you feel comfortable enough to have the talk about the dissolution of your marriage.
I know you are assuming he is going to have an angry response but I would also prepare for him to agree with you.
I know many alcoholics who saw separation/divorce as a new unobstructed open door back into their comfort zone of drinking. That reaction left the spouses unprepared, shocked and unsure of how to handle it. But then of course once the element of finances, spousal/child support/homes/cars/furniture entered the picture it was a whole new ballgame.
I would only have this conversation when you totally feel are can and will stick to your new communication skills. Maybe have some more therapy sessions along with a plan of what happens after you announce this to him?
Will he move out, will you move out? What is your immediate plan?