Shawn always listens.
He's so different from Gus, he always has been. Where Shawn keeps his feelings to himself and never lets anyone else know when he is hurt, Gus needs someone to talk to, someone to support him. Shawn will always be that someone. Because he always listens. Whenever Gus needs him to listen, no matter what, Shawn will. He'll interrupt and crack one-liners and act preoccupied, but they both know Gus has his full attention. Even when he wants to scream 'Dude, get over it!', Shawn listens and gives his friend that shoulder to cry on.
Because no matter how much he doesn't want to admit it, Shawn Spencer cares.