This line of thinking seems most relevant to me, Tara state of mind, behaviors and the known conflicts with MH.
Multiple details like the dates and number of recent interactions don't match with MH statements in the press. He also seemed to really downplay other things that could point suspicion his way, such as he did things with her once in a while over the last year like going to a movie that summer; Dr G has mentioned they went on a trip to Florida together that summer. Things that lower suspicion he emphasized; e.g. she told him she was going to kill herself and that she returned to give him one last hug goodbye.
I would like to know this as well. Early on when press focused on known investigations of AV, MH and HD, an article mentioned a list of 3 additional men Tara had relationships worth investigating. I had posed on the podcast discussion Jim Hickey as one, boyfriend seen at the parade as two, and third unknown? Dr G had offered up the name Stuart Griffin, but haven't seen mention if he was with her at the parade or someone else.