I am a believer of Sonic being kind of shy or touch averse when it comes to physical affection, so I think that even if he was in a relationship with Amy, that fact wouldn’t really change (though maybe he’d be a bit more open to her hugs and kisses so long as they’re not overwhelming or in public)
But when he does choose to show physical affection, it’s probably pretty subtle. The way he often carries Amy like a princess whenever they need to get somewhere fast inspired me to head canon that this is one of the ways he feels comfortable initiating touch- by finding some practical excuse for it hehe
Also, he’s definitely not a fan of PDA, but his arm will subconsciously find its way around Amy. Either by obnoxiously leaning on her or resting a hand on her shoulder
I just like the idea of him keeping a gentle hand on her back or a casual arm draped over her shoulders when he’s relaxed and around their friends 💖💖💖