Man, I still don't understand why she's so devoted to him before. He even had a lover at o...

You have to remember that he (Raymond) was her childhood first everything. Therefore, she thought that she had enough love for both of them.

Raymond, although a person who had only experienced love from his mother, and later Elijah was an emotional cripple person. He friend zoned Elijah and did not realize his true feelings for her.

Keep in mind, we saw glimpse of it when he started the rebellion. He did not turn against his family completely until the First Crown Prince hinted that he was going to kill Elijah (that blonde girl who followed Raymond around). I think he told the Duke and that lead to the Duke being his loyal supporter.