Mastering Sin by Emily Stormbrook

Trapped in the prison of her mind, Ivy Sinclair is forced to relive the horrors endured at her captor’s hand, while desperately fighting to return herself to reality. There is only one mind-set that stops the unbearable memories from surfacing, and the one person she trusts to keep her safe doesn’t understand what she needs.
Miles wants nothing more than to protect her, to make her feel safe and secure, instead he sends her spiralling into the prison of her mind to relive her torment until he had no choice but to seek help from a close friend.
To help the woman he loves, Miles must embrace a part of him he never knew existed to help guide her through her trauma until she feels ready to face what she endured.