Shadow Prophet by Andrea Pearson

Hired to assassinate the woman he loves…

Abel hasn’t seen Lizzie in at least seven years, and his experiences since then have changed him significantly. He’s sure he’s moved past his earlier crush, that he’s immune to her carefree and bubbly personality, but the moment his eyes land on her, he knows he’s still in love.
Instead of a joyful reunion, though, he only suffers agony at being in her presence again.
Because he’s being blackmailed into murdering her.
And there’s no way out. The Shadow Prophet has vowed to kill everyone Abel holds dear if he doesn’t complete the job. Abel has tried everything he can think of to break the contract, but nothing has worked, and he has nowhere to turn.
Complicating things further, he gets recruited by a second client to help Lizzie achieve an impossible mission. One where they must work closely together while hunting immortal demons. One that will either destroy him or force him to kill her before he’s found a way out—before he’s ready to do it.
But how can a man ever be ready to murder the woman he loves?