While I do think she should trust her husband more, the "it's for your own sake" gives the impression that he still doesn't see her as someone that can stand beside him as queen. "...telling her would only recklessly drag her into this" is also annoying because she has already been dragged into it. Leaving her in the dark only makes her more vulnerable imo.
Even if the power shows the truth, the truth she sees are incomplete and missing context. Treating a partial truth as if it is the whole thing is very unwise of her.
At the same time though this is the power that helped her survived so its reasonable she relies heavily towards it. It doesn't help either that Tarkan was never clear to begin with that he has "someone he loves" in the earlier chapters. What he cleared up was that he wasn't in a relationship with Diana but he never fully explained to her that he did have someone he loves (or is looking for).











IMO, it's not over until each of their heads roll