Basically, all these games/novels people get isekai'd into actually exist, and someone on Earth has a dream vision about some events on it and make things based on that.
So maybe the novel's author saw the king approach the saintess and then they have sex and thought 'clearly he consoled her'
When in reality the guy could've been threatening her like "See? It's all because you tried to escape that girl had to die, now be mine or I'll make anyone else who's kind to you suffer" or such :v
Then again in Witch's Heart there was a master and slave relation that seem cold on the outside, but when she was distressed she called out to him and he came rushing for her, the implication is that they are very close but chose to keep up this master/caged slave situation.