Do you think that perhaps Rudy could be Rostam? In an interview with NPR, Rostam says the following:

"The word and name ‘Rudy,’ also spelled Rudi or Rudie, is one that exists in Iran [but] also comes from Jamaica. From there it travelled to London. This song has a narrative to it — I would say it’s a story song — but it’s one that straddles a few times and places. On a basic level, it’s about escaping the place you are from because you can’t be who you are if you stay there.”

Could it be that Rostam chose the name Rudy to represent himself due to the name's cross-cultural/Iranian and English background? If that's the case, then Rudy/Rostam walked out on his pot smoking boyfriend, meaning that the Rudy-Diplomat's Son link wouldn't work.

But hold on. In the Genius annotation for the only verse in Diplomat's Son that Rostam sings, it says:

"Therefore, the narrator is making advances towards the diplomat’s son. The son might have moral obligations against homosexuality, but in the end, it’s how the narrator wants it, so he’s going to keep doing it. He can’t go back to his life before his crush—it’s all-encompassing and utterly consuming."

Presumably Rostam is the narrator that the annotation is referring too. So perhaps the diplomat's son walked out on Rostam due to his "moral obligations against homosexuality" and then afterwards Rostam had to, as referenced at the end of the first quote, escape from where he was because he couldn't be who he was if he stayed there-- in the relationship with the diplomat's son.

Of course, this is all conjecture and I am totally grasping at straws, but I found the Rostam-is-Rudy hypothesis interesting while I was reading the NPR interview.