Okay, I'm hoping someone here can help me find this fic.
I'm pretty sure it was on bjfic.net.
What I remember is that Justin had Multiple personality disorder and Brian was asked in to help him or something. I also vaguely remember that one of Justin's personalities may have killed the gardener because he was abusing him.
Thanks!!
EDIT - Found!! It's 'Maybe This Time' by Ashleigh Kinnerson @
Link to part one. Thanks to both who replied!!