Disclaimer: Once Upon a Time is the property of ABC Studios and Disney-ABC Domestic Television, as well as it's myriad writers and producers. I am none of them and, as such, make no money from this venture.
This is a canon divergence though how, exactly, I leave up to you to infer.
He finds her by the water just as the sun is setting, arms wrapped tightly around herself as she stares at the incoming tide. He can see something is bothering her by the set of her shoulders, and he speeds up, unwilling to let her bear any issue alone.
"Emma," he starts as he draws up beside her, faltering when he sees the look on her face. "What's wrong, lass?"
"I-" She stutters, sea green eyes wide and staring up at him with fear in them.
His chest and hand clench hard in tandem, the leather of his glove creaking like the weathered stays around his heart. Her voice is small and so impossibly young when she finally speaks.
"They want me to… they want me to save them but I don't know how."
His mouth firms and he glares over her shoulder, blue eyes fixed frigidly on the buildings at her back. She keeps talking, trying to justify their madness, and he lets the words wash over him as he tries to rein in his instinct to just take her and the boy and leave this town to their fate.
"What, exactly, are they asking for?"
"They said," she falters, hesitates, and anger boils up in him that they could make her do such a thing with their careless demands. "They said the only thing to break the curse was True Love's Kiss, my True Love's Kiss, but… how can I do that when I don't know what love is?"
His eyes close with her pain and he knows, he knows that this town will break the both of them. They're too demanding of her and he, ever mindful of the ache he gets when she is hurt, is burdened just the same. "Killian," her voice is small and cracks over her words. "Can you tell me what 'I love you' means?"
"I don't know," he says after a silence that stretches a little too long; he sounds as broken as she.
Emma looks up then, the failing light turns her hair into a golden halo and the ocean swirls in her eyes, and he has to look away before he drowns. "I thought I did once - perhaps twice, even - but they left me as you well know, Swan. Even if it wasn't by their choice."
He breathes deep, fingers reaching out to curl in the air just shy of her elbow. "I really don't know what 'I love you' means. I think it means 'Don't leave me here alone.'"
She takes a shuddering breath and sways closer. He brushes her arm lightly and she doesn't pull away. She sighs his name and he feels it in his bones. He steps in, unable to resist the gravity of her presence, and drops his head down to rest his brow against hers. There's nothing else he can say and he hates himself for not being able to give her the answer she sought. Her hands curl in the lapels of his coat, her forehead slipping from his to rest against his collarbone as she uses his leather to hide from the world. His arms come up and around, tucking her in and turning her away from anyone watching inland, perfectly willing to shield her from anything she would ask him to. He feels her jaw move and pulls back slightly to hear what she's saying, muffled as it is.
"Killian," she whispers, soft and vulnerable against his throat, "I love you."
He stills a second in shock, left arm tightening around her waist when she moves to pull away. "Emma," he breathes, fingers twisting in the lock of hair by her cheek, thumb nudging her chin up so he can look her in the eye. "Never."
She searches his face for a long moment before soft sigh escapes her. Her eyes fall closed and she nudges forward, lips brushing his chastely. He's frozen for only a heartbeat but she's already pulling away. He follows, always follows, and gently returns the kiss she'd stolen. "Never," he repeats, breathing it into her until she believes.
They stand there on the beach, sea air swirling around them, until the winds shift and the chill drives them back to the inn. They'll deal with the rest of the town tomorrow.
The clock gently chimes the hour as the sun finally slips below the horizon.