You're cucked

WOW, lo and behold you are cuckolded due to your sister's superior penis size. (who could have guessed?)

This despite your girlfriend being previously heterosexual and your sister's penis being only barely bigger than yours.

You may wonder how this could in any way be enough to make a straight woman be lured into homosexuality, since she is simply being exposed to another woman with a penis that is essentially the same as yours.

You may think to yourself, "The qualities that she finds desirable in a sexual partner are absent here, and as far as anyone is concerned my sister's sexual endowments are almost indistinguishable from my own."

Think again you fucking retard. Your sister has a handful of centimeters on you, and therefore the entirety of the relationship you had with your geef is destroyed upon your girlfriend perceiving your sister's still barely average genitalia.

It's almost as if any appeal to realism made to justify a smaller difference in size being used in these scenarios actually becomes increasingly unrealistic when even an ounce of human understanding is applied.

BUT SURELY NO FUTA FETISHIST WOULD BE AUTISTIC ENOUGH TO BE OVERLY SENSITIVE OF PENIS SIZE WHILE STILL ASSUMING THIS TO BE THE NORMAL REACTION? THEY WOULD HAVE TO BE UNHOLILY CLOCKED WITH DOWNS TO THINK THAT THIS SOMEHOW MAKES MORE SENSE OR THAT APPEALS OF THAT KIND RIGHTFULLY APPLY TO FETISH PORNOGRAPHY.

Don't worry, no one could be that dumb. I'm sure no one has ever made futa porn where a futa's dick was only 1-5 inches bigger than a man's and stole his woman. No human being who has ever encountered and understood their fellow man's behavior could ever be so pants-on-head retarded as to think that somehow this is more realistic than just slightly larger penises.

Great choice. Cause' y'know I myself have definitely decided to be gay upon witnessing a man who has a pretty good singing voice. That's all it takes to wholly warp my sexuality. Your expectations are very realistic and smart and in no way ignore anything about what is actually going on in these relations.