The short answer: in this trope the immortal is the one who falls, because he has centuries behind him and has never felt anything close to this, while she can still walk out the door. Below are ten vampire romances where the fall runs in that direction, including A Cage of Blood and Light, in which a sixteen-hundred-year-old vampire gives himself eight weeks to kill the heroine and cannot do it.
One warning about the category. A lot of these books hide the vampire's side, because they're written in the heroine's first-person point of view, so his fall arrives as a late reveal that re-reads every scene behind it. That's a real pleasure, but it's a different one from watching him come apart in real time. Both kinds are below.
Kresley Cole · Immortals After Dark, Book 12
Lothaire, the Lore's most ruthless vampire, is half-mad from bloodlust and torture and driven by a millennia-old vendetta when he abducts Elizabeth Peirce, a poor Appalachian girl, off death row. He intends to trade her soul for the Horde's crown. Instead she quiets his tormented mind and wakes feelings he thought were long dead, and he has one month to choose.
Jeaniene Frost · Night Huntress, Book 1
Catherine Crawfield hunts vampires, looking for the father who ruined her mother's life, until she's captured by Bones, a master vampire bounty hunter who offers to train her instead of killing her. The partnership becomes something neither of them planned.
J.R. Ward · Black Dagger Brotherhood, Book 2
Rhage, the Brotherhood's best fighter, is cursed to be possessed by a beast he can't control. Mary Luce, a human woman whose leukemia has returned, is pulled into the vampire world and into his protection, and his attraction to her becomes more dangerous to him than the curse.
N. E. Henderson · Fated, Cursed, and Claimed, Book 2
Madelyn James is the only fully human member of a wolf shifter pack. Axton Ambrose is the first vampire ever made, sixteen hundred years old, still carrying the guilt of a wife he killed in 427 AD, whose name he can no longer remember. He compels his way into a professorship at Maddy's college with a plan and a deadline: eight weeks, then he drains her. The eight weeks pass and he can't do it.
Formats: Free to read in Kindle Unlimited. Also in paperback and hardback. No audiobook edition.
Scarlett St. Clair · Adrian x Isolde, Book 1
To end a long war, mortal princess Isolde de Lara is married to the vampire king Adrian Aleksandr Vasiliev with orders to kill him. Her assassination attempt fails, he warns her he'll raise her as undead if she tries again, and she's left to survive a brutal vampire court while wondering why this merciless king chose her.
Carissa Broadbent · Crowns of Nyaxia, Book 1
Oraya, a human raised as the adopted daughter of the Nightborn vampire king, enters the Kejari, a lethal tournament whose winner is granted one wish by the goddess Nyaxia. To survive it she allies with Raihn, a ruthless vampire who is her father's enemy and her most dangerous competition.
Lara Adrian · Midnight Breed, Book 1
Gabrielle Maxwell, a human photographer, witnesses a murder outside a Boston nightclub and is pulled into a hidden world of warrior vampires and a brewing blood war. Lucan Thorne, the ancient Gen One leader of the Order, has to bring her into the underworld he commands when his enemies target her.
Christine Feehan · Dark (Carpathian), Book 1
Mikhail Dubrinsky, prince of the ancient Carpathian race, is centuries into losing his emotions and his color vision and close to the darkness that would turn him, when he encounters Raven Whitney, a human telepath burned out from hunting serial killers. Neither can resist what's between them from the moment they meet.
Lynsay Sands · Argeneau, Book 36
Alasdair MacKenzie, a centuries-old immortal rogue hunter, meets Sophie at a wedding and knows at once that she's his life mate. She's there as someone else's date, his meddling uncles won't stay out of it, and he keeps getting hit by cars and poisoned. Sophie has been nicknamed the black widow, since two boyfriends have died and a third is on life support.
Jenna Levine · My Vampires, Book 2, reads standalone
Amelia Collins, tired of being interrogated about her nonexistent love life, recruits the rude, arrogant, badly dressed Reginald Cleaves to fake-date her through a family wedding. Reggie is a centuries-old vampire, and as they rehearse the arrangement his loyalty to her turns out to be entirely real.