When she turned, she knew she had caught him off guard. He wasn't hiding his emotions well, was showing exactly how he felt. He never did that, would never allow her to see his actual thoughts and feelings unless she had to know, unless it was of some importance. When he spoke of seeing things happen to his team in front of him, she thought back to seeing Owen being shot and dying, that first moment when they had lost him before the glove was found again. She thought back to Tosh dying in front of her, with Jack holding Tosh close. He had to see this all the time, deal with team mates and friends dying in front of him without being able to stop it.
Without thinking, she reached out, her arms going around his waist tightly. She had held back that urge to hold and comfort him for long enough, but she hoped that he would not pull away. She knew that even if he didn't want comforted he'd allow her that small amount of comfort for herself. But for now, she was content with her arms around him, her cheek pressed against his chest.