i don't think she was shown to be in love with him at all
I think there's a little misunderstanding about ML and FL relationship ending. It was him that gave up on them, FL did her job and after the end of the mission she wanted them to overcome what happened, however ML couldn't just go back to what he was before and so he end their relationship.
It kinda makes sense if you think about it his father doesn't huayong to die cuz he has to name another crown…
I do think now, that his affection is fake. He is using ML as bait, because everyone will aim at the Crown Prince, i mean the ML is a bastard so the emperor is using is more disposable son.
One question though…what was the point of the father allowing the FL and SML to get close to each other growing…
It was him that make ML and FL marriage possible, it was his plan that thrown FL to ML view. It's all a plan so his son (2ML) has a motive to fight against ML, and unfortunately 2ML is believing like a duck.