Segur is Ferdinand’s sidekick, and just as much of a pain as his friend. Victor describes him as "a lover of art and a perfect fool," a man who seems to have no purpose and isn’t really good for anything. Plot-wise, he’s important as the owner of the yellow car which ultimately kills Nina. He also helps paint a better picture of Ferdinand, since we get to see the aesthetes’ pretentious and trivial conversations. Probably the most interesting line about Segur is Nina’s exclamation: "Oh, he is such a darling, Segur!" Understandably, this irritates Victor. Nina really does give out affection, as he earlier claimed, to ANYONE, even annoying and useless lovers of "art." Victor adds that this "[does] not commit her to anything." He may be referring to that for Nina, such an exclamation is given without a thought and probably meaningless. Or he may be wondering whether she’s had an affair with Segur. We don’t really have enough information to conclude anything concrete, but Victor, in his jealousy, is probably apt to at least suspect as much.