Outed at school

For starters, I live in a republican state.

I (16m) dated another boy for around a month when I was 11 years old and in the 5th grade. Before we dated, we were friends and he came out as gay and asked me out, and since I was also exploring my sexual identity, I said yes. We ended up breaking up and haven’t talked much since we broke up.

Over the years, I have become not really “popular” but I have a good amount of friends who are considered “popular”. Most of my friends are also homophobic and don’t know I’m bisexual. I have pretended to be straight this whole time and I have tried my best to put this past relationship behind me as I don’t want others to find out.

Recently, my friend (who is homophobic and doesn’t know I’m bi) found out about my past gay relationship and is now telling everyone about it and calling me “gay”. I’m really worried about this since my reputation is on the line. I don’t want others to know that I’m attracted to the same gender.

How should I explain myself without letting all my friends know that I’m bisexual? What should I do? Has anyone else dealt with something like this?