If your boyfriend/girlfriend have twin, would you date or have sex with your boyfriend/girlfriend's twin behind their back?

I don't have any partner or twin but I see a lot of people who have experienced when they're love someone but after they find out their crush has twin, they switch to like that twin instead or they'll like both of them because they can't choose one. I wonder why is possible when all twin have different personalities?

If your boyfriend/girlfriend have twin, would you date or have sex with your boyfriend/girlfriend's twin behind their back?
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