Antidote (Harusari) summary:

Two years ago, the great lord Sylhan was stripped of his title and status, reduced to a life of mania, amnesia, and slavery. He is resigned to his newfound lack of freedom, until a knight appears in front of him. A gentle hand around his waist, sweet lips pressed upon his own, and a deep connection forged in the unknowable past: Sylhan is confused, but unable to stop himself from being drawn ever closer to the mysterious man. The once proud lord can no longer lay claim to glory, wealth, or power…but what about love?