I really felt for Boyega as he is a very talented actor and the movies just... threw Finn's character out the window. Well, I think we have Ryan Johnson to blame for most of it, but JJ Abrams is not spotless either.
The first movie almost immediately forgets that Finn was a kid who was kidnapped from his parents and basically turned into a Jannissary -style child soldier to fight for the First Order. We never get an explanation how he broke his mental conditioning, and a few hours after turning, he is gunning down his fellow stormtroopers without an ounce of regret. Then the movie hints at him maybe being force sensitive, they show his devotion and love to Rey, and... all these are thrown by the wayside and the sequels use him as a comedic character and saddle him with another love interest whom he really does not seem to be into.
When in the third movie he spends the whole movie trying to say something to Rey, I assumed it was that he loves her, but NOPE!
Talk about such a major waste of a character. The closest he has come to having an arc was in a deleted scene where he actually turns some of his fellow stormtroopers against Phasma.