It takes Harry some time to realize he doesn't know who he is actually jealous of, between his brother and his father, and then he has to mentally slap himself for getting jealous in the first place. Besides, for every time Sirius puts a hand on Draco's shoulder, he also ruffles Harry's messy curls, and now that Draco's stopped ignoring him, they spend as much time together as they do with their father.