Most likely because of the second heart he gave her after he almost killed her even though he knew she isn't his Charlotte. He practically imprinted on her and now wants her to have his child as that's how it works with this story's concept of the golden dragon. He forcibly in a way claimed her as his breeding ground as he can't have children with anyone else but her.
Fuck him I don't give a shit about his feelings and the imprinting was non-consensual it's giving Renesmee
At least Renesmee would grow up and make the choice for herself. Here, the MC told him to take it back more than once and already made her choice. He left her with no other option but to run
so why after all the 5 lives she had been, the emperor decided the MC is shasha now???