I find it sad that in 2x08 when Brian's at the gym with Ted and Emmett after finding out Justin kissed a boy at the party and broke their rules. He's going really hard at working out saying he feels out of shape and Ted says to him "Why are you bothered you've got an 18 year old at home" and Emmett replies "He needs to keep him". They start teasing him that Justin will leave him for a younger, cuter guy the ironic thing is that's exactly what Brian's feeling insecure about. So little moments like that you see he does love him and is worried that he could leave him, and finding out Justin kissed someone else after Brian made sure to keep to their rules and turned down anyone who tried to kiss him really hurt him. It was a huge move on Brian's part to make those rules because for the first time in his life, he felt so strongly about someone else that he agreed to some form of monogamy with him. Which then plays into us seeing how heartbroken he is in Season 3 after they split.