Drink if you want to. Make sure you are aware of your motivations when you begin to fix the third cocktail. In my experience, that Third Glass came to represent a turning away from me and away from intimacy. I would choose to drink with her from time to time, but I could not follow her into the nightly oblivion. I wanted a close relationship.
If she drinks the third glass I begin looking for what I'm going to do that evening when she's fallen asleep. If she asks for water, my mind enters into a different set of fantasies that involve her participation. The real joy is that we've had this discussion.
Alone, I am still somewhat of a hungry animal. I contemplate calling my recent ex more frequently than I'd like to imagine. It's a similar story to my previous relationship. Perhaps we can just get our physical needs met without worrying too much about the relationship or the future.