My gf of 6months suggested a Threesome with a girl. We are both 24. Obviously I was like sure and we went about looking for a third party to join us. We carried on talking about it and the subject of trying a Threesome with a male came up. I said I wouldn't like it and as a result she said no Threesomes then because it's a double standard. Funny thing is is that she claims she didn't want to be with another guy anyway but because I wouldn't be cool with it she doesn't want to try a Threesome with a girl.

It turned into an argument (lost frame I know) and I pretty much ruined my chances of having a Threesome with her.

I still want the Threesome but that's not the point. How do I not make this mistake again? How have you guys dealt with this double standard? Is it a double standard? Anyway back from this?