Everything about this situation was wrong. Isaac shouldn't have been this close to Lydia, because she was Lydia Martin and she was Allison Argent's best friend. She was Lydia Martin and she was way out of his league, she could have done so much better than some curly haired bag of insecurities with limited redemption. She was pregnant, and she felt vulnerable with the way things had been going with Stiles. Her body was coursing with hormones that made her feel things she didn't want to feel, and he was emotional, in need of comfort and touch.
Isaac knew enough to know that he shouldn't close the space between them, and that the way she was looking at his mouth had nothing to do with what she actually wanted. He knew enough to know that the way she said his name was a request for space, it must have been, and not an invitation. The only problem was that Isaac didn't know how to convince himself any of that was true.
It hit him with a rush, that bold confidence that he needed to tighten his arm around her waist, and her name barely managed to leave his lips before he did it, throwing everything that he knew he should do out the window and just doing what he wanted. The kiss wasn't chaste. It came with no hesitation, because if he was going to do it, and if she was going to push him away, he wanted to make it count. A hand moved to the side of her face as he dragged her into him, holding her tightly, and her lips were just as soft as he thought they would be. His heart was pounding, because he knew that this wasn't right, and yet he couldn't stop himself. He needed her. Isaac needed her in a way he hadn't needed someone in a very long time, and it made him as weak as it made him terrified.