Are we exclusive?

OK, so basically I have been seeing (but NOT dating) this really cute boy, let's call him X, for 2 years and we really get along well. We're more than friends but less than boyfriend and girlfriend - I guess I'm just not ready for the whole boyfriend thing. But ANYWAY that's not the point of this entry.

See, I have a dilemna. I'm a naturally outgoing person but boys often tend to perceive me as being flirtatious (which I'm not - I don't think...!) and today this boy, let's call him Y, asked me to the cinema. Y has asked me out before and I have told him that X and I are kind of an item, but he really took me off guard today. If he had done it electronically I would have explained that it was my aunt's birthday who was giving birth to octuplets, so naturally I'd be there all day. But he didn't. He asked me on a bus. Full of strangers. So I said yes. But now I'm not sure. I mean, is it as friends? I definately don't think of him as anything more, but who knows if this is mutual? Sure, I want us to be mates that can meet up, but he seems to be implying more. 

Well, here are my options:

A. Call/Text/Facebook him that I will be busy that day, due to my aunt's wedding.

B. Tell X about it and assure him we are just friends (which would be beyond awkward).

C. Tell Y I will meet him, but only as mates.

D. Turn up to the 'date' but look a real state (that unintentionally rhymes..oh dear..) so hopefully this 'allure' will go out faster than the flip of a switch.

Right...so what should I do???!

Maybe it's OK for us to meet up. I saw some pictures of X with a group of girls so maybe we're not exclusive to meeting up with people in the opposite sex.

Oh dear, SOMEBODY HELP!!