Omg you definitely need to get her back! Do whatever it takes. (Within reason if you have to for you own sake)

But in terms of how you can get her back, try calling him out. Ask for him personally. Don’t make a deal. Give him a choice, one that he can’t refuse. If he’s as diplomatic as what I saw in the post, he has to be somewhere between reasonable and logical. (Even if he is the dark prince himself.)

That should be enough to get her back and still you being around at the same time. Please be carful.