Michael is Brian's boyfriend since high school, but then comes Justin

[natkinnat]

I wonder if there's AU fic(s) where Brian and Michael are boyfriends since high school and because Michael digs Brian's personality he accepts open relationship with Brian, as long as there's nothing serious, but tricks. But then comes Justin and there's no vacant "boyfriend" role there at the Brian's side.  And in true Brian's character Brian denies any feelings toward Justin despite his own (Brian's) slips in behavior (actually cheating on Michael). He doesn't lie to Michael, admits that he was wrong, but doesn't promise not to do it again because he knows that it is a promise he can't keep... And the relationship with Michael over the years is a safe place for him, for Brian never actually was on his own, not in a relationship. And they never did friends-only thing with Michael, so there's a huge chance to loose all connection with Michael and his family in case the relationship is over. And then Justin gets bashed and... Something like that.
Did anyone write this kind of story lines?

Update: There're some fics advised.
*Rules of the heart by Shanon Marie is really close enough to what I had in mind.
* What We Break For by Tinkabelle is even closer.

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