Flirting a lot with my closest friend?

It sounds like she's about ready to vault herself on top of a fence post if you don't make a move soon. Sounds like you have a really special relationship. Something most people will never know. It's up to you at this point, she's already let you know how she feels. Everyone is scared of rejection, though, which is probably why she hasn't come right out and say she loves you. What if you didn't feel that same way, and you really were kidding? She's afraid she would scare you off and you wouldn't be friends anymore. So go for it.