Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
My poor heart is sentimental
Not made of wood
I got it bad and that ain't good.
- Duke Ellington, 1941
What's up with the epigraph?
Of course the epigraph for Hotel on the Corner of Bitter and Sweet comes from a jazz song—jazz plays a huge role in the story and is something that Henry, Keiko, Sheldon, and Samantha all love. This particular Duke Ellington quote is all about sentimentality and following one's emotions, even when that might not be the most "sensible" course of action.
This is definitely the case for Henry and Keiko. Even though it would be a lot easier for them to never become friends or sweethearts, Henry and Keiko throw logic to the wind, fighting against an unkind world and Henry's disapproving parents to spend time together. Henry even goes on a Greyhound bus all the way to Idaho in order to visit Keiko and declare his love. Now there's a boy who definitely has it bad.