I don't want to share with a roommate because I feel like it's not reciprocated
Do you think that your roommate does not share with you?
I started to bake brownies for him and he ate all of them secretly when I was in the gym.
Your friend should share those brownies with others. It's wrong to do that and not share.
He shouldn't get any of my brownies. It's mine and it's very delicious. I should hide them from him.
I think that you should talk to him so that you can arrive at a happy medium. I do not think that it is fair to not share with the people that you live with at all.