I have to say Woo-Moon displayed excellent attitude here. It was hilarious when he was about to leave when the girls refused to allow him to proceed alone. It's not like he needs to lord over those two, it was about making the prince alter his orders. Not getting on his knees, refusing the initial government position offer, he just kept doing what I'd have liked to expect him to do, yet was afraid he wouldn't do. It's kind of a pity he still needed to accept the practically no-strings-attached position, but it's understandable with his highest goal being the destruction of Muncheon. It'd be difficult to completely eradicate a large organisation on his own. Not only will he get troops to deal with the many Muncheon grunts, but more importantly he will get intel and connections. Though it's possible some people won't anymore want to associate with him, after he got the official position.
It's no wonder he wanted to refuse the princess. I don't believe he really intended to take things this far with Mara, for the time being, with Muncheon still around, and he definitely didn't want to have Ha with him right now. A harem will do him no good when he's going after a dangerous and unscrupulous entity like Muncheon.