My girlfriend and I have recently been trying ENM. We've only had sex with one other person each so far and we've been very open and honest with our communication. A few days ago she was asking me about the girl I slept with, and asked me if she had a nicer butt than hers. This seemed to come from a place of jealously, and I felt like I was being set up for failure. I decided to go with the honest answer, and say yes. This was really upsetting for her to hear because she explained that she wants me to think that she has the best butt in the world.

Should I have lied to her? Is it a problem that I don't think she has the best butt in the world? I'm struggling to find a way to resolve this with her.