Okay, so, the thing this, neither Arthur or Merlin fall in love with each other.
They’re just VERY VERY VERY best friends. Arthur’s the prince-to-become-king, and Merlin is a sorcerer, who’s called Emrys, and he has to become Arthur’s man servant and disguise the fact that he is a sorcerer to help Arthur in each and every one of his conquests.
The reason why Merlin has to hide his Emrys side is because sorcerers would get killed if the King found out that they were alive, since it was a sorcerer who killed Arthur’s mother.
So yeah, Merlin becomes Arthur’s man servant, and oh my god they both are SO fiercely loyal to each other. They fight like an old married couple. Merlin takes NONE of Arthur’s shit and calls him every name under the Sun, and Arthur has his own way of showing just how much he cares for Merlin! And they both just … urgh, they’re so fond of one another yet they hate each other sometimes! And the entire Kingdom knows they both cannot function, well, Arthur more so cannot function without Merlin!
Ohhhh man, I won’t spoil what happens at the end (you may know? you may not?), but you should watch it.
I’m being toooootally biased here, I know, but URGHHHH, you should watch it!!!