Andrew: Lord of Despair (Lonely Lords #7) by Grace Burrowes

Andrew Alexander will do anything to protect those he loves...

After a tragic yachting accident leaves him wracked with guilt and despair, Andrew Alexander becomes certain he doesn't deserve to be around his own family, let alone the beautiful, forthright Astrid Worthington. He wanders for years, only allowing himself respite from his self-imposed exile when he thinks Astrid safely married. He returns home to find instead that the only woman he's ever loved has been recently - and mysteriously - widowed.

...especially from himself.

When Andrew leaves, Astrid refuses to pine. She finds an amiable husband and contents herself with a cordial if unexciting marriage. But her husband's sudden death and Andrew's reappearance threaten to break her heart all over again. When Astrid's life is threatened, she finds Andrew will do anything to protect her not only from her enemies, but also from the truth of his dark past.