What if the fact that Cora didn't have a heart while she was pregnant with Regina impacted Regina's ability to love. As we have all seen Regina does love but in a very twisted way; she seems to lack the understanding of the meaning of love. She is ready to take Henry away and pull the trigger on the curse and let everyone else Henry loves die. Which Henry would never forgive her for. And I do realize that she loved once with Daniel but that was true love and since it is the strongest magic of all it works a bit differently. So in short my theory is that because she was born to a heartless mother, the thing she will always crave most is love yet the thing she can never truly do herself is love. At least not in the same way Emma and MM can. Regina will only ever be able to love twisted. Thoughts?
Ruby on the other hand was upset of what she had done to Peter, but she didn't have Rumple to teach her the dark acts of magic. She also learned in the episode "Child of the moon." How to control her wolf form. Yes, she might nit have a chance at love but she did make the most of it to have lots of friends. Like Snow or the dwarves.