I think tattoo face is the Demon King. Why would he have a tattoo on his face if he wasn’t? Or some sort of wizard, but leaning more on Demon King. Furthermore, Demon King & The ML are probably working together to protect MC. The Demon King obviously has some connection to MC, as he continues to appear in her dreams & refers to her as Jun.
There have been a whole bunch of theories. Some of them being that the ML has also reincarnated several times over. Which explains why he’s more insistent on staying by her side. It’s been brought up that she’s suffered immensely in her past life, she’s been raped, killed, & drank poison to end it all. From this, I do assume that the MC was intentionally left behind for her own protection in that village. And in one chapter the MC pointed out that his marriage to the princess isn’t exactly what it may have appeared to be. So ML may have never fallen in love with those other women, so his reasoning could have been for political reasons or to distance the MC from people who could harm her.
There’s been speculation, I say speculation because all of the theories I’ve read so far are from people who can’t read Japanese. And after taking a look at chapter 20 w/o full context, it feels that just something doesn’t quite add up. If the Demon King is the original hero (I can’t take a look at the previous chapters), then he & the current ML cannot be exactly the same person. So I’ve begun to wonder if the ML is an extension of himself. I just want to make sense of their connection/relationship. And Jun who died, I suppose the original MC to the Demon King isn’t exactly our MC. I guess what I’m getting at here, is that the ML & MC have their own relationship, it feels all to distant from the Demon King & Jun. I can’t foresee the Demon King rekindling any form of romantic relationship with the MC.