You're right. That curse is taking a toll on both of them and also to their bodies. Ain't no way the Prince will forgive himself if he brought harm to Myungha considering how he is gentle and considerate of him. If it continues like this I'm scared they may part ways.
If you think about it, the Prince is being SA'd too
He very clearly wants no part in this, but his body is being used for sexual purposes despite his best efforts. It's genuinely kind of sad