Being as the "original plot" of the novel had them as the perfect couple until 4 years in the war had him fall in love at first sight with the FL of the "original plot"- dumping and killing her off as a side character.
Now Erika is the FL- or at least she is still "Erika" the side character who was written for the prince. It makes sense she'd be "suitable" for him.
I very much like the complexity between this plot and the supposed "original plot" dynamics. The author is doing a great job actually making you feel that the characters "orginal relationships" status quo. This are a little different from "Orginal plot" events, but the character's core are the same. Good job Author!!!
I think the fl is more suitable to the black haired guy