Six weeks into Camelot things started to go batshit. That's why Emma Swan cast that curse.
It was one crucial moment that failed her. It wasn't everyone, it was just someone.
Emma thought it would be different but she was miserably wrong. When she kissed Regina that moment in Camelot she really expected it to break the Dark One's curse. Emma thought that moment was the perfect time for Regina to admit that she loves her back.
Emma thought that kissing her will make her admit that she's in love with her as well, but Regina's shocked face… her reaction was something Emma couldn't take. In that moment instead of pulling out all of her darkness it just darkened her more. Because; what's darker than a heartbreak?
"You don't think I have it in me?" Regina asked Emma while they were facing each other at the docks.
"I know you don't." Emma answered back, but it only made her heart ache inside of her.
Emma knows Regina can't possibly be the savior of this town, because her curse can only be broken by a true love's kiss. No one in this, or any other world, can love Emma. Not like that, not ever. If anything, that kiss they shared in Camelot only showed Emma how lonely she's always been and forever will be.
Her family loves her, sure. But it will never be what she was so sure to have with Regina. She could bet her life on it. Actually, she did bet her life on it. That's why she became dark.
She sells them a lie that only sounds true when she speaks to Regina. Because it is, in fact, only true when it comes to her. She can't possibly admit that Regina failed her in front of everybody; that would imply she cares about Regina's intentions and feelings. It's just Henry that she can't lie to; she cannot tell her son that he failed her. He'd know she's lying to him.
Regina's shocked face came seconds after Emma put her lips against hers. Everyone could tell that Regina was not expecting Emma to choose her as the one person to break her curse when the moment came. She was given the choice, and she chose Regina over anyone else.
Regina pushed her immediately, a little too hard then she intended. In that moment Emma was blinded by her emotions. She saw Regina's horrified look on her face. She saw her brows clenching, she looked at her and in a matter of seconds she saw Regina panicking.
Regina's eyes weren't focusing on Emma; she was focused on everyone else's stare, and then looked down as if she wanted to hide herself. Emma could feel how embarrassed Regina was at that moment that she kissed her.
Regina's fingers touched her lips, tears started to gather in her eyes, and her lips were starting to part slowly from each other in awe. She took one or two step backwards – at that point Emma couldn't tell. She only saw Regina's expressions and felt as if both of them could compete at who is going to be the first woman to transport herself out of there.
A sword jabbed Emma in her stomach. The biggest and sharpest sword ever was stuck inside Emma's black heart.
But Emma just froze because her heart was broken, violated. After that it was a matter of seconds before she realized what a terrible mistake that was to even try that. She didn't think it through, but the next thing she saw was herself in a black leather outfit, in Storybrooke, in front of every single member of her family not knowing what had just happened.
When she told Regina, "Too bad there isn't a savior in this town" it was her pain talking. Her broken heart that knows this curse cannot be broken because Regina doesn't love her back. Emma knew this curse will never be broken, because Regina pushed her back. She took a step back from her kiss; she did not love her back. There is no savior for this curse because there isn't one true love for her at all.
Little did Emma know then how miserably and terribly wrong she was.
Regina couldn't break the Dark One's curse at that moment in Camelot because Emma just came out of nowhere. It was so sudden to her that it made her startle. At the time Regina was still trying to convince herself that the hooded guy was her so called soul mate, and she was sure that Emma has found love with her own leather loving pirate.
Regina herself was in denial of how much love she had for Emma.
In the next few weeks Regina would fight so hard to get her own memories back. She'd fight so hard against Emma Swan that just looking at her as the Dark One would be so painful for her that she'd realize how much she really cares for her. How desperate she is to see the Emma she knows and loves coming back.
When Regina Mills would be out of ideas anymore, she'd just go to see Emma one last time, and when they'd be the two of them alone, she'd confess her love for Emma by the truest love's kiss ever.
In that moment in Camelot it wasn't a justified heartbreak for Emma, because what truth she thought she knew was completely false. Regina didn't take a step back because she didn't love her, she stepped back because she knew she loved Emma that much, that her own heart might not be able to contain her insane emotions that were running inside of her.
Regina loved Emma that much. Too much… it was the biggest misinterpretation ever, because of two women that were too blinded by their own insane love for each other. Two broken hearts that healed each other; and eventually broke the terrible curse by the truest true love's kiss.