Hemingway isn't meant to be understood in the usual manner. He was far deeper than that and often a little boozed up when crafting new creations.
Did I ever tell you about my grandfather's somewhat questionable autobiography where he claims to have walked the streets of Paris with Hemingway pumping him for information on how to become a successful writer?
Yeah, probably didn't; but, now that I did I'm too tired to do your homework.
Read the story over again, notice what the waiters are saying as the soldier
and girl go by, there you will find a clue. Hemingway drops clues everywhere usually in a subtle way....the story was written in the 1920s, this would be a good time for you to crack open that history book and see what life was like at that intersection of time. Yup, more clues in that.
Time is a common theme in many tales, it is your challenge to discover what it means in this case. Think about the mention of consideration of suicide, drunkenness and 'possibly only insomnia', they connect, dwell on it for a short while, the answer will come to you.
(or you could just cheat the old fashioned way and open up your sparknotes...which is available at fine computers everywhere)