How can I convince my girlfriend to let me have sex with her sister❓?❓?

I still love my girlfriend and everything, but her sister is so sexy and I just want to do it one time. How can I convince her?
I want my boyfriend to have sex with my sister
I'd be okay with my boyfriend sleeping with my sister just one time
If my boyfriend slept with my sister just one time, I'd be upset but I'd get over it
I wouldn't be okay with my boyfriend sleeping with my sister just one time
Not sure/other
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It's really important.
How can I convince my girlfriend to let me have sex with her sister❓?❓?
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