I'm on mobile so I can't be arsed to type a long message. I'll keep it short and add details later if you guys need it.

 I'm 25 years old male and my gf is 26 years old and we have an open relationship, so there is no cheating involved in this case. Here's the the situation: I have a one-night stand with someone and I make it clear that this is purely a one-night stand with no purpose of seeing each other ever again and they want the same thing. Everybody just wants sex and everyone is on the same page here. BUT I'm not telling the other person that I'm in a relationship. Since it's just a one-time thing and everybody is getting what they want, I don't see the problem here. If I wanted a FWB thing or something more or if I led someone on then they obviously would have the right to know about my gf.

But some friends told me that in their opinion the other person "always has the right to know" about my girlfriend, even if it's a ONS. And it's assholish to not inform them. My GF always informs others about her open relationship even with a ONS, and that's perfectly fine. She also thinks it would be polite if I did the same, although she doesn't think I'm an asshole like her friends say. But AITA if I don't do the same?

I swear this isn't a validation post if someone thinks that, I'm seriously curious since I didn't see the problem and others called me an asshole.