Odo doesn't need to eat food, but he can
done so in the past, remarking that it was "messy". But he can simulate
breakfast, as you'll see.
Odo is not a human, and doesn't have the same hang-ups and beliefs that humans do. So Garak tortured Odo - big deal. It was awkward for both of them, and Odo understood Garak's desire to return not just to Cardassia, but to his old life in the Obsidian Order. It wasn't a sadistic act on Garak's part, and Odo understood it. If somehow the roles had been reverse, well, maybe Odo would've reluctantly tortured Garak, too. Maybe.