The Lass He Left Behind by Jayne Castel

He thought he’d forget her. He was wrong. When a battle-hardened warrior returns home from years of campaigning, he discovers that the lass he left behind never married—a lass who will be his undoing. Second chance and redemption on Medieval Isle of Mull.
After a decade campaigning against the English, Loch Maclean returns to the Isle of Mull to find his father dead and his lands in disarray. Cattle thieving is rife, and the isle’s clans are at each other’s throats. Loch’s got his work cut out for him—but he’s distracted by a woman from his past.
Mairi Macquarie is even more beguiling than he remembers, only these days she’s no longer innocent and biddable. These days, she’s got no time for him at all. Or so it seems.
Mairi was heartbroken when the laird’s roguish son went off to war and never came home. She got on with her life and tried to forget him. But now he’s back, battle-hardened, and cynical—and even more dangerous than ever.