I didn’t realize that I was bisexual until I was older than that.
Until I was 24, I thought I was straight.....then I thought I was gay for the next couple of years, until I realized that I was still attracted to women as well (I was close to 27 when I determined that I was actually bisexual).
I’m not stupid (and I don’t think you are either).....but for me, coming to terms with my actual sexuality was a journey.