There was one glaring clue. One enormous mistake, which could ONLY have been made deliberately. Andy took a sharp, deep breath as the enormity of what he'd just seen and heard, hit him hard. [This is definitely my sandbox. But I've borrowed the toys.]
Provenza's tendency to underestimate Andy Flynn is about to bite him on the ass.
Somewhat AU (Alternate Universe) Loosely beginning in the Closer era. AI's Sharon O'Dwyer and Major Crimes Andy Flynn hate each other. But do they? Ladies & gents it's called "Fanfiction" for a reason. Don't like it? Don't read it - it's really that simple.
Slightly AU in that events are different from the original timeline. Andy collapses in Sharon's office and is rushed to hospital. Sharon realises how empty her life will be if he doesn't make it and confesses to Provenza just how much she loves him, thereby redefining for Provenza what the word IDIOT means.
My own take on the letter Andy wrote prior to his surgery. The letter we never got to see.
Andrea insists on hearing the minutiae behind Sharon's glazed stare, and will not take no for an answer.