It seems to me that knowledge of psychology is more important than knowledge of history when it comes to writing romance. I have read plenty of romance novels that contained not a lick of history in them, save that necessary to convey the setting accurately, while the romance novels that most interest me are chock-full of psychology. They are are all about how two people have internal conflicts or internal issues which cause misunderstandings with each other, so that, thorough the book, the misunderstandings are resolved, and the couple come to a happy resolution, understanding each other well enough and trusting each other enough to admit that they love each other and to move forward.
So, while I will certainly acquaint myself with the history of the Regency period, I will focus much more on knowing psychology. Probably reading some books on marriage counseling and mining Quora for plots would help a lot. I've noticed that many people who answer questions on Quora tell stories--and when they do, these answers get much higher like counts, because people like to hear stories, especially heartwarming ones, much more than they like to merely get answers to their questions.