Even though Mulan was completely misguided, even though she had almost ruined Emma's chances at escape and damned the people of Storybrooke to an existence with Cora in it, but Emma forgave her because she could tell that everything Mulan did, she did for her friend. It was something that Emma admired, it reminded Emma of the only good quality that she knew she possessed, mixed in with her numerous faults and shortcomings, was nobility, and every time that Emma was near Mulan, she was reminded of that. Mulan made her feel like maybe she was still destined to make her mark on the world. Which is why, no matter how much of a liability Mulan was to keep around, Emma couldn't bear to cut her loose. She gave Emma hope for the future, a feeling that Emma had never experienced before.
Mulan admired Emma. She admired her courage and loyalty, but most of all, she admired Emma's inability to hide her big heart no matter how hard she tried. She reminded Mulan of a girl that she had been courting. There were a lot of memories there, good and bad. She was the one girl who Mulan thought might finally be able to love her, but unfortunately, Mulan had been wrong. She had disappointed Mulan, just like Mulan's sexist, condescending parents. She had broken Mulan's heart, proven to her that she was unlovable. It was the worst feeling that she had ever experienced, and Mulan had vowed that she would never allow anyone to break her heart again.
"I need to go find Phillip." Aurora stated after they had escaped from Rumplestiltskin's cell. "Would you like to come Mulan?" Aurora asked her with thinly veiled hope in her voice. Mulan was sorry to disappoint her friend but she had devoted years of her life to the quest of finding and saving Aurora. She wasn't ready to devote years more of her life to another. She still wanted
to explore places other than her little corner of the world, but she wasn't ready for another quest.
"No, my time for quests is over for now." Aurora looked like she was trying to hide her disappointment, but she perked up after Snow White spoke.
"I'll come. True love is the most important thing to have in your life. I'll help you find it." Snow White smiled at Aurora. "But first we have to help Emma get back to Storybrooke."
"Aren't you coming back with me, to see David?" Emma asked.
"No, I've already found my love. I can't be selfish. If I can help Aurora find her love, that's what I have to do."
It was that kind of love that allowed them to defeat Cora and Hook. It wasn't just their fighting skills or the fact that Hook and Cora underestimated them that they were able to beat Cora, it was also their belief in and capacity for love. It was also for that reason, that Mulan and Emma kissed right before they jumped into the portal. After Aurora and Snow White had left on their own quest, Emma and Mulan were so overwhelmed by their joy at finally being able to escape that they kissed each other, their passion having no other way to escape. Neither one of them were usually spontaneous or sentimental people, but the emotional tsunami of finally being free with a person that they had started to fall in love with just washed over them. Mulan pulled away, breathless, then they jumped into the portal, without any idea of what changes they would face once they had gone through it.
The world was so different from anything that Mulan had ever seen in the past, yet it was oddly familiar. She could see elements of her world in it, but everything was off. The trees weren't as green, the sky, not as blue, but despite all of this, Mulan loved it. She could escape from her past fears, without any reminders that they had ever existed. She kissed Emma again, and again, and for days, Mulan was happy, she was content. Until she got too comfortable, until the situation started to become a painful reminder of her past heartbreak. Every kiss, a memory of a previous kiss. Every touch, a phantom of where she'd been touched in the past. Every minute that she was with Emma reminded her of her past relationship, and it wasn't just the good parts anymore. She was reliving pain that she had pushed down a long time ago to keep herself sane. She was remembering the way that she had been used, the way that she had been shown that no one could possibly love her. So she left. She ran away from her pain the way that she always had done and probably always would do. Running was her defense mechanism and she had been doing it so long that she didn't know what would happen to her if she stopped. No one could sustain love for her, and she didn't want to give anyone the chance to prove it to her. She wanted to keep that shadow of a doubt. She wanted to have the tiniest hope that maybe, eventually, someone could love her. Even if she didn't deserve it. She wanted to keep her tiny scrap of hope for love intact, so she left. She didn't remember how to love, but she did remember how to doubt. She told herself that Emma would never love her, because nobody could. Mulan left Emma because she knew that she didn't deserve love, and she knew that Emma would stop loving her. Maybe not tomorrow, maybe not the day after that, or in a month, or in a year, but eventually Emma would fall out of love with her, and leave her, just as everyone else had. Emma would worm her way into Mulan's heart, then once Mulan had completely given up who she was to be with her. She would leave, and Mulan would finally see the heartbreaking truth that she had always known in her heart of hearts, that she was unlovable. So she left. She chose to sacrifice the woman who might possibly be the love of her life for security. Due to her own decisions, Mulan was alone. Just as she always had been and always would be.