when emma came to her with unexpected, but welcome offer to date, regina thought it was her second chance. an opportunity to start all over again and forget how many terrible things she had done in the enchanted forest.
later it became clear the ghosts of the past wouldn't let mills go anyway. never. that's why she began to doubt the validity of their decision.
and she doubted exactly until emma said she'd go from darkness to light not just next to regina, but with regina. at that moment, mills realized the blond sheriff wasn't just a chance, she was a prize that regina — evil queen — didn't deserved.
she tried desperately to find the old desire to push away anyone who came within a step of the walls, but she couldn't. because emma is special. you don't want to go to expensive restaurants and talk about politics or the weather with her. with emma, you want to walk barefoot in the rain, and then spend a week at home with a cold, making tea with raspberries for two, putting aside the anger and grumbling, because it was definitly worth it.
swan often said that regina is under her protection, whether it was angry citizens or david with a sword at the ready (because his daughter spends too much time with their family's mortal enemy) or from a scary spider on the kitchen floor. and for the first time in many, many years mills truly believed she could love and be loved.
regina had no idea how she could hate her true love. she loved emma so much now that she wanted to shout it out to the whole world, but the queen only whispered it in the sheriff's ear under the cover of night, because Emma and Henry were her world.
they were very happy together, and it was expressed in small things. after all, they are together, and this is right.
regina knows no matter how much she destroys herself, no matter how much she drowns in memories and darkness, emma will always come, say the cherised "I believe in you" and everything will fall into place again.
emma ignited the spark of love and life that everyone around regina (and especially regina herself) was trying to extinguish. but swan carefully keep the light inside the queen, and soon she became a spark of regina's dark heart herself, for which she wanted to try to become a better person.
because she loves.
because she is loved.
because she is happy.
and to hell with anyone who says villians can't have happy endings.