I would be very scared about coming out at school. I would wait until university, as I would expect there to be much better support groups and you'd be making new friends anyway. I think university (or equivalent) is the accepted place to experiment and find yourself.

However, if you are determined to come out right away, I would still advise some caution. Frankly, I would do this in a cowardly and manipulative way!

I would start with a barefaced lie: "I've just found out my cousin is a lesbian. I don't know how I feel about that. What do you think?" You would find out a lot about your friends without committing yourself.

Your fictitious cousin is going to need a name, an age and a city to live in. ("I overheard my parents talking about it. I'm not supposed to know.") And word could get back to your parents, so it might blow up in your face. But coming out straight away is even riskier.