AIO that my gf passed her girlfriend privileges to one of her friends?

Sorry in advance for grammar mistakes, english is not my mother tongue.

I'm 26 years old (male) and I live in a very unusual relationship. I don't wanna make it a fetish or sexual related post, but for context I have to talk about it a little bit. If it's not your cup of tea, please stop reading.

My gf is into feedism, and I'm into bdsm (I'm a sub), so actually we are a pretty good match. I'm under her dominance 24/7 without safeword. This means that I have to eat exactly what she says, and the amount of food that she says. Even if I don't like it, or even if it too much. If I'm "bad" she makes me eat until it hurts.

I know it sounds stupid, but please don't judge us, we love it and we are happy in it, and I know that we're weird, I don't expect you to understand us.

I have never ever questioned her commands, I always obeyed no matter what, because that's how we work, and we are in this for 1.5 years.

But today we were at the mcdonalds with her friends (two female friends), and while we were waiting in the line one of her friends (call her Kim) asked my girlfriend that is this a good time for her (Kim) to control me, like they talked about it earlier. My girlfriend said yes, but you'll pay his food then. "Sure thing".

She ordered insane amount of food. I ate, but there was a point where I had to stop, and Kim asked my girlfriend that is he allowed to stop? My girlfriend replied with a no, and Kim said that she wanna see me eat until I vomit. Fortunately my gf stopped her.

Story ends, I kinda confronted with my girlfriend afterwards, and she reminded me that we live like this. And I agreed, but there is one thing that she controls me, and there is another thing that some other person do the same in a cruel way like this.

Sorry for being too visual, but am I overreacting?