Gideon's too shaken by the entire experience to offer to help Amos finish. Teasing him during the act was about the most he was capable of, without a moment or two to recover--and by the time he realizes Amos has taken himself in hand, Amos' breath is moving over his skin, and he's disinclined to interrupt him. The most he does is wrap his arms loosely around him, both palms moving over his hair.