Should I wait until I'm in a relationship to come out?

I'm not out to a lot of people because I feel a bit uncomfortable calling myself a lesbian and my sexuality doesn't seem to be relevant most of the time. I kind of feel like the best time to come out will be when I'm in a relationship.
I'm not too sure I will be able to find a relationship if I'm closeted. I have tried coming out when I was fourteen, but most people thought it was just a phase.
I kind of want "proof" before I come out. I'm not even 100% sure if I'm a lesbian yet. I kind of want to call myself a lesbian because I want to date girls and I don't really want to date guys, but it's hard to be sure of myself. It also feels wrong to call myself bisexual.