Nightcurse by Emma Hinds

Cursed with eternity, haunted by love - discover the truth about living forever in this queer enemies-to-lovers romantasy with a magical mystery at its heart, for fans of Juno Dawson and VE Schwab. Emrys Swift is so dead. 157 years' worth of dead, to be exact.

And eternity feels even longer when you're cursed to be seventeen forever, hidden from the world in a magical library, and desperate to remember how you died. But when ancient spellbooks go missing, Emrys must join forces with annoyingly attractive shapeshifter, Aubrey Vale, to solve the mystery. Which would be fine...if they weren't (im)mortal enemies.

As they tangle with ghosts and battle mermaids, can they outrun the secrets of Emrys's death and Aubrey's life? And is it possible to fall in love when you're already dead?