One of my most solid head canons for Graffiti Pete and Sonny is inspired by a play I saw Robin in a few months ago. Sonny still sometimes gets anxiety attacks. Especially at night. Music makes him feel better when he's nervous. If Sonny wakes up from a nightmare, or when he's anxious in general, Pete puts on slow, instrumental music. He hugs Sonny, and they just kind of slow dance until Sonny feels better.
Poor boy can barely sleep on those nights and Pete just holds him and kinda rocks while he calms down.