William can't say for certain what it is about the way Archie nods that makes the tension he didn't realize he'd been holding in his shoulders melt away, but he believes it may have something to do with his boyishness, his confidence, his enthusiasm for this and... many, many other things. It was that that drew William to him in the first place; with Horatio, it was his seriousness, his dedication.

To feel that seriousness breaking down in his arms, to feel that dedication shifting — it makes his head spin, to the point that he tightens his hold on Horatio, closing whatever space was left between them.

When he turns his head, it's to kiss Horatio's curls.

When he seeks out Archie's attention again, it's to urge him, through gaze alone, to join them.