The Favor by Suzanne Wright

Vienna Stratton knew she only had herself to blame. You didn’t let yourself become indebted to a man like Dane Davenport, no matter how badly you needed his help. As his personal assistant, she was very aware that the globally successful CEO was ruthless and unforgiving.
Of course, if she’d known he’d request that she be his wife for twelve months, she’d have hesitated in accepting his help. Because what she’d learned from Dane was that the devil wasn’t ugly and terrorising. He was seductive and captivating. He hummed with whispers of temptation – the temptation to sin and surrender, to let him brand and possess you. He awakened every need and fantasy you had.

He could even make you love him.