Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
In his poem “Wanted” Humbert Humbert (the narrator and main character in VN's novel Lolita, 1955) says that he is dying of hate and remorse:
Dying, dying, Lolita Haze,
Of hate and remorse, I'm dying.
And again my hairy fist I raise,
And again I hear you crying. (2.25)