Who is Sumner Lee from That Summer and what is their importance?

Sumner Lee is Ashley's ex-boyfriend from the summer after tenth grade. He constantly stumbles into adventures, and Haven remembers him because she liked her sister while Ashley had been dating Sumner. When he reappears, Haven looks to Sumner to somehow fix the past because she blames her family's problems on Ashley dumping Sumner. When Haven finally learns that Ashley broke up with Sumner because he cheated on her, she is disappointed in him. Sumner is the first boy to break Ashley's heart and the first boy to disappoint Haven.