I think that the question is, does Justin want to know Brian has him in a whole separate category and that sex with them is not "just sex," as you say here, or... does Justin want monogamy, if not now, then at some point. And if Justin does want monogamy, there are two questions to ask:

Why does he want it, in other words, for what reason or purpose, and two, why, when Brian offered it to him, did he not like it and even somewhat reject it, in season 5?

Don't answer that, though, because we're getting into that thing where talking about the themes in my stories messes up my writing process. Shhhh.