Just rewatching the documentary and just before 4 mins in, Lisa is explaining to Omar her thought process for what will be the main dilemma/ crux of the show, and it made me realise what exactly Simon was saying when he broke up with Wille at the end of Episode 5. He was saying: I've seen what the monarchy does to you and how it hurts you, I've experienced it myself, so I have additional empathy for how that must feel for you. Also, I, too, am being hurt by it (see all of season 3 when he's not smiling with Wille). I thought I could try it out for your sake to see if I could handle it because you're worth it.
But after spending the birthday day with Prince Wilhelm and the Royal Court, he sees that it will continue to hurt both of them, and there will be no respite, things will only get worse. He has seen Wille get worse right in front of him on that day. It is poisoning Wille, and he is becoming someone he doesn't recognise. Simon decides that he does not want that to happen to either of them. The only thing he can do is leave the system so it can stop hurting him. Unfortunately, because Wille is entwined with Prince Wilhelm, it means he has to leave Wille too.
To me, by staying with Wille, Simon is condoning bad behaviour or the status quo by just going along with everything the Royal Court says while they both slowly deteriorate. So though he leaves Wille to save himself, he is also saving Wille because he is showing Wille that this is not alright, boundaries have to be put in place somewhere and Wille needs to start setting some boundaries for himself too. If Wille thought that Simon would stick around to support him and occasionally be someone he could lash out to, then he may not have felt the need to save himself from the monarchy. Because Simon is around to hold him up.
So for King Wilhelm truthers, Simon is required to know his place as an aid to the King, whilst suppressing his own pain and never putting pressure on the King by asking for help with his own issues. There is never a time when they would be equal in their relationship, even in private, because everything about Simon's values, ambitions, and passions would have to be deleted. King Wilhelm's needs would come first. This is what class does. It sets up hierarchies of certain humans' needs being more important than others and even that certain humans are superior/supreme to others. Therefore, to function, it needs lackeys who know their place to serve those on top. Hillerska, as an institution, is a mirror of Simon's relationship as a partner for the next king. Hillerska being closed is the equivalent of Lisa abolishing the monarchy. (By the way, there's a real-life incident of the 16 year old Prince of Denmark having to be removed from his elite school when issues of sexual abuse and other scandals came to light. This happened in 2022).
On a side note, this made me think about the Duke's role as consort and imagine that that would be Simon's role to model himself on. If we want Wille to remain as a Crown Prince and have his boyfriend, do we want Simon to become as bland and ineffective as the Duke is, where all of his focus is solely on the Queen's needs. Smoothing over any rough patches with innane conversation and totally neglecting and not 'seeing' his child. Simon deserves to be himself, as does Wille.