The queen is completely shameless. If I remember correctly, she promised him that he would not need to take the role of a king, with half the reason she said that was as a negotiation tactic ("benefits without responsibility") and the other half to prevent him from taking away power from her. Bit by bit, she throws responsibility after responsibility on him, constantly breaking her promise, and has him still play the role of a side-king, working only for her benefit.
Every time, Zenjirou kept his promise of not grabbing any power for himself, and yet he is expected to do perform all kinds of duties that he is completely unprepared for, all the while being confined to the palace. Every time she tells him to do something, she pulls a guilty expression and says she is sorry, yet she keeps on doing it. At this point, Zenjirou looks to me more like a glorified servant with some perks under house arrest than any king I've seen.
Zenjirou gave her advanced knowledge from his world, technology, a son and works for her. And what does he get in return? Having sex every once in a while? Eat some tasty food? And Zenjirou seems to dismiss the fact that she simply can't bring herself to keep her promise as "it can't be helped" or maybe internalizing it as it being his "duty".
Bitch, the deal was simple. You gave her a son and kept your hands to yourself when it came to power-grabbing and in exchange you got to live a life of luxury without worries. Someone's clearly being conned here.
Correct me if I'm mistaken about anything.