Kushiel's Avatar by Jacqueline Carey

Second Hand 

The triumphant conclusion to this trilogy, Kushiel’s Avatar by Jacqueline Carey is a sumptuous fantasy of defiance and redemption – perfect for fans of Sarah J. Maas and Jennifer L. Armentrout.

Phèdre nó Delaunay is a woman touched by Kushiel’s dart, chosen to forever experience pain and pleasure as one. Her path has been a strange and dangerous one, and through it all the devoted swordsman Joscelin has been at her side. Her very nature is torturous for them both, but he is sworn to her and he has never forsaken his vow: to protect and serve.

Now Phèdre’s plans will put his pledge to the ultimate test. For she hasn’t forgotten her childhood friend Hyacinthe, and has spent ten long years searching for the key to free him from eternal indenture. But this is a bargain ...