I haven’t seen any meta on this, but I think something about the last episode kind of went under the radar while we analyzed it.

Fitz has had complete screaming breakdowns before in Jemma’s presence. The blatant temper tantrum he pitches after they discover Koenig’s body is heartbreaking, of course; he’s lost control over himself entirely, he’s making an enormous fuss, throwing things and screaming because his emotions have completely overwhelmed him. 

Triplett and Phil both seem completely shocked by the breakdown, but Jemma just goes to him. She doesn’t react with surprise at all. He’s lost control of his emotions like this before in front of her, and she knows how to handle it.