Stuart Lamarack, played by Dave Foley. A client of Will's who becomes Jack's longest relationship, until Jack cheats on him.

Jack has countless short-term lovers over the course of the series (and presumably long before and after), although most are never mentioned by name (or mentioned at all, it is constantly assumed, and not always stated, that he has mulitple boyfriends in every episode). Due to Jack's hilarious promiscuity and his habit of forgetting his boyfriends' names it would be literally impossible to list all of his love interests over the course of the show.

Will once joked that if he was to avoid every man that Jack had ever slept with, "That would leave me with...women!"