So ONE sexual partner means she knows what sex would have been like (different) with any others??

Also in the 90s all women were wearing boxers, it was a thing.

Also, long before the 90s, lots of women were wearing men's boxers and briefs in the late stages of pregnancy and after giving birth.

Amazingly, I have been wearing boxers most of my life. Still female.

Same. I have no bottom to speak of and women's knickers fall off me. Not a good look whatever you're wearing.