She kissed me!!!??? My bestfriend kissed me. Help.?

I'm typing this quickly. Sorry if I sound illiterate. We are both 16 year old girls. She has always known that i'm the least phobic person in the world, and i've never actually told her but I think she figured out that i'm biual. She never liked talking about ual orientation and was quick to deny it when I pointed out that she was looking at our female teachers bum (I was joking). We have even had a conversation about how we'd react if our 'friend' kissed us. She has only ever had one boyfriend and is quite reserved, but I love her. I've had boyfriendS and am quite a lot more outgoing than her. I'm a flirty person. I'm very close to this friend and yesterday we went to the cinema together. She seemed to be acting really weird. She kissed me! I was shocked, didn't really kiss her back and just turned back to the screen. She was silent while we walked home, and chose to text me instead of talking to me. She confessed that she liked me. I know it must've taken her A LOT to tell me that because it's so 'not her'. The thing is... I don't like her back. Sh*t. She knows i'm , she has told me that she's always liked me even though she tried not to. I wish I liked her back. Telling her that it's not mutual will crush her and send her back into denial. Argh!