Unfortunately, at this point I honestly think the endgame for the poor Prince is probably suicide.
He chose to marry her. He chose to side with her over his family. He walked into this.
But I think it's pretty clear at this point that she's just going to use him until he's used up, and then get rid of him, and say and do whatever is needed in the press to destroy him the rest of the way as she goes. After that, I kind of doubt he's going to see himself as having much left to live for.
This outcome is not certain, but it's looking increasingly likely.