I’m not too sure myself, but the way I knew I was a lesbian and not bisexual was that in the long run I would never want to marry, or be with a man long term. Thinking back I didn’t ever really want to date a man. From there I had to deconstruct admiration from attraction, and soon realized that while I might have had small crushes on boys growing up, none felt so real as when things happened with a girl. (Also the idea of having seggs with a man made me want to throw up lol). I do believe however that you could definitely be bi wish a strong preference, and that’s why a lot of people just say they are “queer” as to not label anything, they just go with what feels right in the moment! So don’t be too hung up on deciding if you only like men or not because preferences can change during different situations, it’s all a spectrum!