When I was in jr high school me and my friends would talk about how sonic never really showed any signs of trauma after fighting the bio lizard with shadow.
I had the idea that what if, sonic had trauma flashes after seeing Lancelot cuz he's shadow's alternate universe self. As in a happier version of shadow.
Sonic of course would of done his best to save shadow from falling to earth (or that portal thing?) but I'm sure sonic would of still blamed himself for shadow's temporary disappearance.
Sonic probably thought shadow would have a better happier life if he had caught him. So deep down he blames himself and rarely shows it. That's my theory anyway.