The Goodbye Wish by Barrie Farris

Josseran is a medieval lay brother who swears he’s a virgin to the mystic setting up a summoning spell. Trysts with men don’t count, right? Wrong. The spell miscasts and bonds Josseran and a blue lizard to an amulet forcing them to serve whoever wears it.
Hal is an ambitious young historian with two quests—solving the great mysteries of the past and losing his V-card. Accidentally inheriting a bespelled amulet, he acquires a fascinating manservant who grants unlimited good wishes.
Turns out that magic exists and is responsible for many of life’s strangest mysteries.
Josseran doesn’t live inside the amulet until summoned. He’s moving in as Hal’s very visible roommate. Brawny, gorgeous, and fully equipped to please, Josseran is delighted to serve a cute male owner after centuries of selfish mistresses who regard him as a creature, not a man.
But fun times are limited. Only a virgin has the power to free Josseran by making an extraordinary wish to help mankind—and it must include the sacrifice of a personal dream. Owners call it the goodbye wish, because if granted, the spell breaks. Then it’s goodbye to the owner’s privileged life… and goodbye to Josseran who will cross into the afterlife.
Is giving up Josseran a personal sacrifice? Nope. Not that easy. Whatever Hal sacrifices must directly enable a wish that aids mankind. So far nothing connects.
Every miscast spell will break if the right thread is snipped. The one binding Josseran is a doozy.