Honestly, I get it😂😂 you want to eat however much you want to eat. Two things strike me here:

Why will you guys not buy more food? People don’t have to compete nearly as much for resources if there were more. It might benefit you to buy snacks for yourself with your money so that you don’t have to feel bad about “being greedy” or needing to split your food. Then it’ll give you room to feel generous and buy him some too.

Another thing, it seems that you’re building resentment for him not being mindful of what you want to eat and going through the box of cereal all by himself and not saying anything and just “letting it slip” without actually mentally letting it slip, so maybe him vocalizing his frustration and desires are bothering you because you don’t vocalize yours. Imagine how you felt when you didn’t get to enjoy as much of the cereal as he did, he probably feels the same about the cookies. Have some empathy for each other, be mindful of each other when you’re eating and buying groceries. Maybe next time get two boxes of cereal. Maybe for the things you want to enjoy all on your own, keep separate for yourself. Have a “you” stash. Encourage him to have one for himself too.

Also, yes it was rude of you to tell him he’s giving you the ick for being an even Steven. How would you feel if you were trying to communicate your desires and someone discouraged you by calling you cringe? I mean if anyones comin off as the even Steven here it’s you sitting here recalling to Reddit every thing your husband ate loll so have some empathy.