How did you know?

So I'm 14 and lately I haven't been feeling comfortable in my own skin. I don't know if I'm bi or not. I've never really been attracted to girls, only guys, that I can remember.

I don't really want to come out to my family yet, for 2 reasons:

1. If I'm bi, then I'm scared my dad and brother won't except me.

2. I don't want to come out and it end up not being true.

So how did you know!?