How about the horrible, disgusting way Sean treats Gus and the fact that Gus just takes it because he's too meek/dependant/messed-up or something to get away from that.
You can call it cute and say they stay with each other because of friendship, but honestly, I've yet to see Sean do one single thing to/for Gus that would actually be an act of friendship, without spoiling it or doing it for his own gain in secret.
It's disturbing and terrifying.