The whistle broke, and that's what this sentence means from now on.

The sound image of the whistle is a cruise ship about to set sail, and "heartbroken" describes the deep sadness. Combined with the last sentence "I travel alone in the world", the meaning of this sentence is easy to understand: the author is about to leave his hometown, and from the moment the cruise ship sets sail, he will lead a wandering life. I think that I can only wander alone in the future, and it is difficult to see my relatives and friends in my hometown, so it means oil tanker.