Juliet.
He watches her closely, risking more than just a glance. At first he didn't think much of her. When she first came here, Lassiter was still getting over his last partner. She had come from Miami, so she had to deal with all new people, and Lassiter wasn't the best for making her feel welcome. Or, making anyone feel welcome for that matter. But as time passed, he began to feel changes, little things. He felt more of a need to protect her when they were in the field. He pinned that on just growing closer to her as partners. He felt a twinge of pride choke his heart when she made a good shot, arrested someone, or stood up for herself. He began to enjoy watching her do everything she does. Type on the computer, file notes, and especially watch her in the shooting range. He felt horrible when he made her upset, even worse than he felt with anyone else, and he always wanted to make up right away.
But he didn't. It was an image thing. Make her apologize, or stay mad, as much as it hurt him to see her upset. Soon he realized that the feelings he was having were more than just partner to partner. He found himself attracted to her. But, he thought, who wouldn't? So again he blamed it on being normal routine feelings, because everything was routine, and that's how it needed to stay.
Shawn was not routine. Shawn dating Juliet was absolutely not routine. It upset Lassiter to see them together, how he obviously didn't deserve her, he was so immature. She needed a real man, a mature man who has his own car and doesn't borrow his friend's credit card for everything. A real man who took care of himself as well as his girlfriend. That man wasn't Shawn.
Another thing that made him think was the fact that she called him Carlton. No one ever called him Carlton except his ex-wife, and he actually preferred it over Lassiter. It made him feel like he was something more to her, something special.
Carlton.
He thinks she doesn't notice him watching her on occasion. But she notices. Not every time, after all, he is trained. But occasionally she'll catch him sneaking a glance, but she never says anything. She kind of likes it. She knows he likes that she calls him Carlton, and that's mostly why she does it.
When she first saw him on her way in to the police department on her first day, she couldn't help but glance twice. The well-kept look, the sexy salt and pepper hair, the way he lifts his head and turns his neck when he straightens his tie makes her heart flutter. In the early days of their partnership, she found herself glancing twice at many things he did. She notices that she had feelings well before he did. She accepted these feelings, and also the fact that it could never happen. He, on the other hand, refused to accept it. Again, an image thing, his own image of himself didn't include falling for a coworker.
She did like Shawn. He was attractive, funny, and he loved her. But Shawn wouldn't be able to provide the way Carlton could. She knew that, too. She knew that she'd rather be with Carlton than Shawn right now, but she had no idea how to make that happen, and what if he didn't really want her? What if the glances and gestures were really nothing at all? What if she accepted her feelings and confronted him about it, to turn out he was disgusted and requested a new partner? She would be heartbroken, and she knows she's had her share of that.
So the two that could be Lassiet, would never be because of each of their own fears. So they thrived on the glances, the subtle gestures, because that's all they would ever get.