I'm thinking that in season 1, Robby and Langdon's relationship outside of work was very one sided. I think Langdon would do anything to get Robby's attention and when Robby finally says 'okay come over' Langdon would feel an enormous amount of anxious fall off of his shoulders
I think everything they do sexually would be on Robby's terms and it would just be Langdon on his knees sucking Robby off and the act would never be reciprocated by Robby and to Langdon it doesn't matter. he's just happy to have Robby's attention for a short amount of time
it's messy and it's toxic but everyone at work goes on about how he's Robby's golden boy so it makes him feel good. reassures him and dampens the anxiety
but when Dennis comes along, it's a whole different story. Langdon is pushed out, especially after the whole benzo incident. he could see that Robby's eyes were trained on Dennis the minute he walked in on his first day. Robby's energy changed instantly.
Langdon could feel the somewhat of a connection with Robby slipping away, fast. it was too late though. Robby was already planning his moves in his head on how he'd lure Dennis in
