How did Quasimodo know that Esmeralda wasn't in love with him?
He had a hunch.
Quasimodo wanted to go on a date with Esmeralda
So he put an ad in the paper to find somebody to ring the bell. A man responded to the ad. He was a man without arms, so Quasimodo politely asked how he would ring the bells. The man said "let me show you", so they went up to the bell tower to give it a try.
The man got a running start, jump...
"I think I have something seriously wrong with my spine" said Quasimodo
"What makes you think that?" asked Esmeralda.
"Just a hunch"