I agree completely about Justin's bravery and figurative balls being a huge drawing factor for Brian. He probably does not encounter much of that in Bablyon/the baths. Justin's courage and outright nerve are major factors in Brian's interest in him throughout their relationship, particularly the very crucial early Season 1. Another late example of this is Brian being so ticked that Justin may actually choose Dartmouth in 118. The dialogue for the "Forever Young" scene is indicative of how Brian feels when Justin may back down from his usual bravery to do what it takes to get what he wants.