Fight for This by Suki Fleet

Can a fairy who can’t control his glamour and the growly Guardian who adores him save the Veil that protects all fairykind?
Grey and Si have been dancing around one another for months.
Grey’s helpless attraction to fairies (and one fairy in particular) is a source of endless frustration—but as his energy can damage a fairy’s glamour, he can’t let himself get close.
Si is different to other fairies and he’s wearing down Grey’s defences. When Si discovers the Veil is thinning around the school where they both work—putting the students and teachers there at risk from detection—he needs Grey’s help to fix it.
Problem is, Si isn’t a true fairy, he’s just a magical mistake. For as long as he can remember all his glamour has done is messed up and broken stuff. Though Grey maybe older and wiser about a lot of things in the human world, he’s pretty clueless about all things magical. He doesn’t even know the Veil exists until Si knocks himself unconscious trying to save Grey’s reputation after a night out.
But it’s funny how mistakes work out. Even funnier how trusting one another can help even the most impossible events turn out all right.