I'm rooting for Green boy to end up with Aristia.
They can even each other out with her gentle nature and his hidden dark one? He seems to really care and even love her and by his actions he would go further and beyond for her. So I hope they end up together(￣∇￣")
I figured that the Emperor would suggest a marriage between him and the Mc, especially now that she is free to be wedded. Or maybe with someone from his kingdom since it would enable our Mc to stay in the Empire under his control.
Or after the kidnapping if it is successful, he could try and have her married with a bonding type magic or something close to a curse.
I mean if u want her that badly that's the route I can see working in his favor ╮(￣▽￣)╭