i'm such an asshole

so like i moved out to college and everything's been going kinda well except for this one thing. my roommate and i are supposed to split grocery bills but he never seems to pay his half on time or even mention it. last week, we got some snacks together that i thought were split 50/50 but turns out it was all me footing the bill. i called him out on it in a text but he said it's because he has an emergency fund thing going on and can't spend extra money right now. whatever. anyway, so today we went grocery shopping again and while we were at it, i saw this cool new cereal that i wanted to try but knew my roommate wouldn't go for it. so i snuck the box under his bag of groceries when he wasn't looking and put a note in there saying we're splitting it even though it's just me who wants it. like why did i do this? now he'll probably get mad at me, or worse, be like okay but i'm not cool with it. i feel so petty for doing something like that but man, i wanted that cereal too much. maybe i should tell him and give him his share back or what. idk. im such an asshole sometimes.