So why does Noctis like him so much anyways?
The whole “he doesn’t treat me like a Prince” is obvious, but so many people act that way towards him (Dino, Vyv, Ardyn, Aranea, Ravus, every side quest person ever…) but they don’t get along quite the same. I think it goes beyond mutual interests (like dogs and video games) too.
One of the reasons why Noctis likes Prompto so much is because he feels like he’s needed around him. Like he’s doing something right.
Imagine growing up, the ever incompetent Prince who can’t even clean up his own candy wrappers, and who had little to no interest in politics. He’s catered to his whole life, and disappointed so many people in his life.
Then there’s Prompto, who’s a little needy, clingy and an obvious klutz, and Noctis finds himself on the other end of the spectrum.
Prompto tumbles and falls in the middle of a link strike: Noctis catches him and flicks his forehead. Tells him to be careful.
Prompto trips and hits the ground while they’re out camping: Noctis bends down, puts the camera away and makes sure he’s alright.
And Prompto thanks him so much throughout the game, when other people are just constantly berating him. Like he needs to focus more, get stronger, make better decisions. But with Prompto, his life seems a little less like it’s falling apart, because for once, he actually feels like he’s in a position to help someone else, and using his own power. For once, Noctis is good enough for someone too. He even caters to him (at least, if you let him) like taking random pictures, heading to the closest hotel when he’s tired, actually heading for the chocobo races, etc.
I mean, Prompto wants to be seaside supermodels? That’s really gay, but if that’s what Prompto wants, then Prompto will get it. Anything for Prompto.
Tldr; the real prince in the relationship is Prompto.