The whole idea that bisexual folks can’t be monogamous because they’re attracted to more than one gender is just so blatantly stupid on its face. Have you ever, in your life, found more than one individual attractive? Then by that token you can’t be monogamous either. Have you ever found two people attractive that you found to be different from each other in some way, perhaps in age or physical appearance or interests or personality? Then, guess what, you can’t be monogamous either! This has been a PSA.
I know where this comes from, though. It’s simple gender essentialism. It’s the idea that gender is SO FUCKING IMPORTANT that if you happen to be attracted to more than one, you can “never be satisfied” without dating people of multiple genders simultaneously.