My (22F) new roommate (26M) is upset that we aren't sharing finances. How can I explain this to him?

I'm not sure if he's never had a roommate situation before or what, but my new roommate seems to think we should be sharing finances.

He invited me to go grocery shopping with him which I'd figured was just a nice gesture to get both of our shopping done with one car and one trip. But when we got to the grocery store he put all of his stuff in the cart mixed in with my stuff and expected me to pay for his food and mine! Which I only learned when we were already at the cashier ringing up. He hadn't even brought his money. I gingerly brought it up after the fact that every roommate I've ever had before, we buy our own groceries. And he seemed alright with it.

Then about a week later I came home and he has made an entire meal with all of my groceries and offered me some food, as if it wasn't my food in the first place. Again I just kindly asked if he could ask me before using my stuff. Thought he was okay with it.

Then two days ago he texts me and says he paid the full amount of rent (since this is the first month we start paying) and I can give him my half to repay him. Every roommate I've had in the past, we paid each half of our rent separately and my one landlord was even adamant about it being that way. So I told him that, he said it was fine and he'd remember for next month.

But now he's being passive aggressive and ignoring me. I don't understand why he thinks any of this is anything to get upset over. I make my paycheck to support myself, not him!! How do I get that through his head? And how can I fix this relationship now?

TL;DR: New roommate has been ignoring me because I've asked him that we pay rent and groceries separately and for him not to eat my food without asking. How do I get him to understand without ruining this friendship even more? I really don't want to live with someone I don't like being around

Submitted December 29, 2018 at 12:58PM by ThinkTide http://bit.ly/2QWskXy