In the short story ‘the Deep’ by Anthony Doerr, Tom is a young man with a serius heart disease that might not live longer.
The metaphors and similes are used in the story to show how Tom’s emotions got his best every time he was with Ruby. Because of his disease, he has been forbidden to have any excitement in life. When he meets Ruby it all changes, for she causes great exciting effects on him so he faints and is advised to think of something blue everytime to avoid the faints. This color became a metaphor to him to calm him down as a "calming sea in the turmoil of life".
Tom would feel "as if the whole sky was rushing through the open door into his mouth" or that "his blood was storming through its lightless tunnels" as metaphors showing his great strong feelings for her before his faintings or that his life only had meaning or 'light' because of her. Also a simile used, for example, when "he was trembling like a needle to a pole" showing his excitement in their adventures.
It can be understood by the use of the figurative languages (making impossible comparisons) in the story that he started to enjoy life and his best self only with her around. He would not care about anything else.