Based on Ruby Slippers (s04e21):
Jane: "You solved a murder. You booked three scumbags, as you coppers like to say. You should be very proud."
Lisbon: "I don't think I've ever been so depressed about a case."
Jane: "You want some tea?"
Lisbon: "I don't think tea's gonna do it."
Jane: "Hm. In that case, I think I know just the thing to cheer you up."
He looked her in the eyes. For a few seconds, he smiled, but then stoped, like someone waking up from a beautiful dream. Lisbon faced him, a little scared of what he was thinking and what he was going to do.
It's uncertain how long, it seemed like forever, but they just stayed standing there, looking to each other. She would never expect what he was going to do. She always believed she was the only one who had feelings between them, but this thought was wrong, and the "angry little princess" was going to discover that.
Jane was nervous, his hands were shaking, but he decided he had to do it. He didn't want to hide those feelings anymore, and he knew Lisbon feel the same way about him. After all, pretend or hide things from Jane wouldn't work, he always realize. When she's sad, he know, when she's happy, he know, and if she's in love, with him, it's not even hard to Jane find out.
He walked two, maybe three steps to stay close to her. Still looking in the eyes, he curved his neck – Lisbon gets so small, and close to him, she gets smaller – and their foreheads touched. They kissed. It took a long time, but they were finally kissing. Lisbon hadn't words, she got emotional, trying not to cry. Even with their eyes closed, it was easy to know the meaning of those expressions. It was happiness. Jane started smiling. Without opening eyes, with fingers crossed, the couple stayed there together. They stayed quiet. They didn't say a word. It wasn't necessary.