I really don't like the part about stories like this when the beating up actually becomes hurtful to the masochist and the sadist doesn't notice or refuses to, it almost always leads to there, but I'll still be reading
I think that will be the whole point of the story tbh, along with them helping each other unravel their trauma that led them to be acting like this. Most likely, the angst will come because of a turning point like the one you described in their relationshiop
The blood of the Truyde family is the black potion—the punishment for consuming the body of the king.