In "Home", Sam revealed to Dean that he had visions of Jessica's death before it happened, blaming himself for not telling her or doing something about it. This was also the secret that he used to summon Bloody Mary in the episode "Bloody Mary".

Sam Sweeney\n\n Jess played along and they began a no-strings-attached  relationship, which continued after he found out she wasn't Katie. With time, their relationship went from casual to serious, but they broke up after he learned that Jess and Nick had kissed.