Is It Wrong to Eat Food Off Someone's Plate Without Asking?

My partner Alex regularly reaches over and takes food off my plate at restaurants without asking. Fries, bites of my sandwich, pieces of chicken — it happens every time we eat out. I've asked Alex to stop multiple times. Alex says "we're a couple, sharing food is normal" and that I'm being territorial about something silly. I said it's not about the food, it's about respect and boundaries. I always offer food when I want to share — I just want to be asked first. Alex says asking your own partner for a fry is "weird and formal." Last night at dinner Alex did it again and I moved my plate. Alex got upset and said I made them feel "gross." I love sharing food. I just want it to be my choice, not a free-for-all.