Yes - funnily enough, I think that by the end of S3 Brian was ready to make a fairly strong commitment to Justin. But then in canon the whole Pink Posse thing happened - and I suspect that Justin's absolute disregard of Brian's feelings during that whole phase undermined a lot of Brian's always fragile confidence in their relationship and then, of course, the cancer thing happened, and then LA, and and and ...

In Experiment, I got to play with my ideas of how it might have gone without all that manufactured drama. :)