Spoiler (mouse over to view)
It's complex. There is romance between Ryuuki and Shurei, but she can't have children, so she pushes him away. Sorry if that's a spoiler, but that's piece of the plot - Why she feels Ryuuki should give up on her and marry someone else. But, I read a translation of a recent light novel. She did tell Ryuuki about it and she agreed to marry him, but he would have to agree to have a concubine have his heir. Over the series, she does have many men after her affections, but she ignores them all - pretty much.