Why did her mother broke up w/ him again? They love each other right?

I heard it was something to do with the dukes wife

Spoiler a lil bit
I can't recall the full accuracy of it but...
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The lady the Duke ended up marrying is the reason. I think that she threatened or tried to kill Rose's beat friend who she later married and that Iris thinks was her father.

Thinking about it.mm.
I think the eye color hiding was due to making sure the Dukes wife doesn't find out and try to kill Iris