Now that I’m thinking about it , laenor had no choice but to roll with rhae and daemon’s plan. They wanted to get married and the only way was for him to die. He would have had to watch his back constantly if he refused, have had to sleep with one eye open or he could have snitched then who knows what happens
He gave up a lot to roll with their plan
In his mind he gained more. He's away from a society he can't be himself in, he's with someone he truly cares about, he can't do the thing he really wants to do which is be a warrior because he's got royal responsibilities and his sister (who probably was one of the few people he could talk to freely) is dead.
Dude was a liability to begin with getting him out the frame was the best move for all parties involved.