I love this little shot because it reveals so much. Everyone's left, even Buck's date. The party is a bust. But who stayed behind? Eddie, who has his ass solidly parked on the banquette, doesn't look at the door even once and who clearly never even considered the idea of leaving like the others. Eddie knew Chimney didn't want the party to start with; he reminded Buck of that seconds after this shot. Eddie is there for BUCK.
Eddie Diaz, who probably has the most conservative and conventional wardrobe of all the mains on the show, bought himself an improbable (and probably expensive) pink suit, which HE suggested and coordinated with his best friend, arranged a sleepover for his kid, and got to the karaoke place earlier than everyone else...but still got told by Buck that he was late, which means Buck expected him even earlier and therefore Eddie probably helped him organize the whole thing. He did all of that for a party that, because he is not as willfully oblivious as Buck, he probably suspected Chimney might not attend. He did it because Buck had his heart set on it for some reason and he wanted to make him happy.
Eddie is there purely for Buck. They're each other's ride or die. No matter the way the party was to go, Eddie was always going to stay. And Buck knows that on some level, because you can see in his attitude that he's taking for granted that Eddie is staying, too. They're a unit and they're in this together.
