essentially, it'd involve that line between doctor/patient that they can't cross. it's been an ongoing thing since he first sought her for help with his ptsd and wherever he's at in the treatment of it is open, but she's essentially made herself emotionally unavailable to everyone but him and they haven't crossed that physical line because she's made sure to keep it from crossing that line. so how they got in so deep is up for discussion and then the rest is open so it can develop organically.