AITA for reacting this way?

I'm a F25 in a 2 year relationship with a F30. I took her out to eat at a restaurant and we both got our drinks as well as an appetizer. Things were going great, we were talking and eating. Then the main courses came. I got a steak with Mac and cheese and some mashed potatoes with shrimp. While she had a chicken and rice Mediterranean bowl. She started digging into her food as did I. I was cutting up my steak into big pieces when she got her fork and took some of my Mac and cheese and came back for seconds. At first I was like okay, it's alright and offered her more if she wanted and she did. But what really did it for me is as I was eating my steak she went and grabbed a shrimp with her fork. I was irritated at first, but shrugged it off until not even a minute later she put her fork on my plate and grabbed a piece of my steak. I immediately got angry and snapped at her. I told her to stop taking my food and to at least ask. She told me she just wanted to taste it. But she's had my dish before. The rest of the dinner was pretty quiet with just small talk here and there. At the end when I was paying the check she asked if I was full or not. Making me feel as if she understood her actions. We went home that night not really talking much. She seemed to be giving me some silent treatment. I feel as though I've communicated my boundaries before and this isn't the first time, but I can't help but feel like an asshole.

I understand there's a difference when someone is close to you as in a wife/gf/mother/brother, yet to me I would react the same way to anyone doing the same action.