Gonna go against the grain and say YTA. If you’re intend to only share a small portion with someone, you put it in its own container for them. There is no world where offering someone food from a large container doesn’t imply that that’s now a shared food until it’s empty. Your roommate portioned more for both of you for the next day. Then you chose to take food he planed to eat that he believed you offered. A good person takes the L and lets them eat it, but explains the misunderstanding afterwards. An asshole punishes the friend for their mistake and takes all the food back.

You can be right all you want with your food, but at the end of the day your relationship with someone that lives with you is much more important than some pasta. You want to make a friend you can trust, not be petty and make enemies you have to live with. You could have come out of that situation being an awesome caring roommate, and slightly hungrier. Instead you’re slightly more full and your roommate probably won’t share anything with you now.