Tagged Yang Yung-tsai according to the cast listing.
This character introduces himself as Sun Tsu, Ho Wing-cheung's character according to the cast listing, but it certainly looks like a different actor. Maybe there was some double-crossing and impersonation going on in the story or maybe the actor was replaced at some point.
江湖了斷 is a common phrase that does not literally translate, whose use is dependent upon context. And "jiang hu" (江湖) specifically in the context of ancient martial arts films/tv-dramas represents the "milieu" or "martial-arts world" in which the story is set. Some in English might call it "the scene" as in the music scene, or the martial arts, scene, etc. In a more contemporary setting and screenplay, among other things, it can mean the criminal underground.