What is so awful about being bisexual? Compared to being a lesbian, it has a lot of disadvantages but also it has its own perks. I wouldn't have it any other way, despite all the problems and frustration it causes. I wouldn't have felt the sort of love I feel for both sexes if I hadn't been born this way. I can't 'have' my female friend as a partner, but that sexual spark makes me all the more devoted to her, even if it gets frustrated. Likewise, I wouldn't have fallen in love with my boyfriend if I wasn't into men. Take it from me, it's not the end of the world to be bi (even if the mental illness rate for bisexuals is shocking).
Anyway, I think you're probably not bi. I think you are scared of not being right about who you are - am I correct? This fear is what is causing you to second-guess yourself. You're allowed to change your mind about this stuff - only a***holes will judge you for it.
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Zombies, zombies will tear us apart...again.