It is shown in "Bleeding Through" that they had met and had a connection. Leopold actually did love Cora, up until he found out she was hiding a pregnancy and lying about it and even stole to keep it secret. That kind of ended things. Cora in the episode "The Miller's Daughter.", tells Mr. Gold that he was the only man she ever really loved. And in "We are Both", she even encouraged her own daughter to kill Leopold as (in quote) "He's not a very strong man", meaning that Cora was only using him to become royalty, or just scorned that he cast her out and chose the woman that exposed her instead.
It's entirely possible that she thought she loved him at the time. Maybe when she met Rumple she realized what real love was (poor Henry!) but had thought she loved Leopold (or Jonathon as well...) and then scorn took over. When someone you loved (or believed you loved) hurts you, you want to do everything to hurt them back.