Perhaps one day, thinking precisely of this hour, of this gloomy hour in which I wait, stooping, for it to be time to get on the train, perhaps I shall feel my heart beat faster and say to myself: "That was the day, that was the hour, when it all started." And I might succeed—in the past, nothing but the past—in accepting myself.
Night falls. On the second floor of the Hotel Printania two windows have just lighted up. The building-yard of the New Station smells strongly of damp wood: tomorrow it will rain in Bouville. (33.58-59)
It's not accurate to say that Antoine is filled with hope at the end of Nausea. But the guy definitely feels better about his life than he has for the past fifty pages. After much consideration, he has decided to give up his history project and write a novel instead.
He wants to write a novel because he thinks that it will help give shape to his life and give him a sense of purpose. Most importantly, though, he wants to write a novel because hopefully, in the future, he'll be able to look back on it and have a clear idea of the person he was when he wrote it. This, Antoine thinks, is the only way he'll learn to accept himself.
After he makes this decision, Antoine looks up at the Hotel Printania, which has been his home for the past three years. He sees two lights turn on and realizes that he is already leaving behind the man that he's been for the past three years.
He is embarking on something new, and he hopes that some day in the future he'll be able to look back on this moment as the beginning of something important. After all, making a fresh start is the best thing you can do when you're trying to create meaning in a universe that isn't giving you any help.