Justin thinks Brian would be making a bigger mistake than Justin did in leaving if Brian didn't take him back. And he also thinks if Brian had any brains at all, he wouldn't have ever let him leave in the first place. And Brian thinks Justin's the one who had the balls to get them back together. And Justin had the balls to do it, because Justin knows Brian loves him and would keep loving him even if he were gone--Oh, and because of Daphne ;P