Why had he let her go? Even as he asked himself the question, he knew the answer. It was that damned connection he felt to her. It had made him feel possessive of her. As he had known he would, Snoke had demanded that he bring her to him.
Defiance had immediately flared in him, and he had tamped down on it and gone to obey. His relief when he saw that she had managed to escape had enraged him, and he had let out his frustration over the situation by venting his fury on the room.
He had known that Hux would delight in telling Snoke about his infatuation with the girl, and he had still played right into his rival's hands. Not only had he failed to get the information they needed, but he had also allowed her to escape. It was all because he felt a bond with her that shouldn't exist. He had told her not to be afraid, but he was the one who should have been afraid of it.
It had caused him to make all the wrong decisions about her. He should have been ruthless about getting the information from her instead of engaging in a slow seduction that had yielded no results. Especially after Hux had called him a besotted schoolboy, he should have tortured her to prove to Snoke that she was only a means to an end. He would have had the map, and she would have been in Snoke's hands.
Instead, she had been free to distract him even during his ultimate test of allegiance to the First Order. Yet seeing her there had also reinforced what he must do. He had been weak with her, but now he would cast aside that weakness and show his strength. She was watching him as she stood beside that traitor. He would wound her now as he had been unable to do directly, and he would destroy the bond they shared just as surely as he severed his connection to his father.
Killing Han Solo affected him more deeply than he had anticipated, and he wasn't as fully on guard as he should have been. It allowed the enemy to wound him, but the stormtroopers fired at them and made them flee. Kylo rallied and went after them.
He caught up to Rey and the traitor. Did he need any more proof that she was his enemy? "We're not done yet," he said.
She looked at him with all the hurt and betrayal she felt. "You're a monster!"
"It's just us now. Han Solo can't save you," he taunted, wanting her to hate him.
She appeared momentarily stunned by his cruelty, and then she reacted with an attempt to kill him. He sent her flying into a tree, and she crumpled to the ground. The traitor called out her name in a panic. Kylo turned his attention to him to finish him off, but he was shocked to see the weapon he wielded.
"That lightsaber. It belongs to me!"
"Come get it," the traitor challenged.
He put up a brave fight and even landed a blow, but he was no match for Kylo. Then it was just him and Rey as she impressed him again with her innate ability and power. She fought him with Luke's lightsaber after snatching it away from Kylo with the use of the force. This was what she could do without training, and it excited him to think what she might be capable of with instruction. She was proving to be his match in so many things, and it was thrilling in a way that nothing had been in so long.
"You need a teacher. I can show you the ways of the force" he offered even as they battled.
"The force," she repeated and closed her eyes.
It was in that moment that he could have easily struck her down, but he still wanted her to join him. She no longer had any such illusions about him, and she attacked him with a ferocity that took him completely by surprise. She slashed his face and beat him down, but she hesitated to deliver the killing strike. Then she rushed off and left him there.
So it was still not finished between them. He had dreams about sinking into her body as she moaned in pleasure. That didn't trouble him, because those were only desires of the flesh. Once he had even gotten a glimpse of one of her dreams about him. He had woken up in the middle of the night and suddenly felt that connection to her. The vivid image that came to him was of him cupping Rey's breasts from behind as she stood naked before his bed. He was instantly hard even as he lost the brief image.
Rey was having erotic dreams about him. The realization made him so hot for her that he resorted to masturbation to relieve some of his sexual frustration. It wasn't enough, and he had no opportunity to try to use a substitute woman in her place during the completion of his training with Snoke. He knew that it wouldn't have worked anyway. He wanted Rey.
She was still a distraction to him. More than that, he was drawn to her through that bond, and that was the real problem. It weakened him, and he must sever it completely. He knew that there was only one way to do that. He had to kill Rey.