Leo protected his heart.
A sense of humor coated the true bitterness inside. He flirted around to show he was okay, but he knew no one took him seriously. He counted on it.
Because, when people saw the true him, all of the hatred and rejection, they were scared. As they should be.
Hazel saw through him. She comforted and protected him. He was willing to shed his bitterness for her, but she was already claimed. She looked back at her boyfriend, and he knew.
Hazel left. Leo withdrew further into his shell.
One more rejection he just couldn't handle.