It’s really making me wonder if he keep MC around so someone who deserves revenge can kill him when all his work is done. He seems to have a strong will to live going off when he talked about being a soldier but would he really keep around someone he knows wants to kill him just for sex if he wasn’t on some level okay with it?
Ohhhh wait that's a nice theory. While he doesn't look like the type to off himself, he comes across as someone who has this "noble" notion of redeeming himself from the sins he has committed through death, at least to me. But hey, who knows what the author is cooking? Only time will tell.
From what I see, having the mc as his somewhat of a concubine comes across as a typical "keep your friends close and your enemies closer" type of thing, especially when he has an inkling that the mc is more intelligent and cunning than he lets on. If he already has an idea that the mc is a mole, he will likely use him to uncover other traitors who are plotting against him.
Took me this long to realize how the love interest is making himself out to be the necessary evil in order to suppress an uprising and stabilize the kingdom. In a way, it reminds me of Lelouch but they just have different goals.