I met a girl who tells my friends she likes me but doesn't want a relationship, but when she's with me nothing happens! She goes all weird, and quiet, and leaves the room as soon as possible! I've seen her with other guys she classes as friends and is all warm and friendly but with me it's just awkward! I like her but never get the opportunity to say it to her. Were apart from each other now and may never see one and other again, should I write a letter stating how I feel for her and leave my number or just move on?

How old are you both and how long have you known her?
Why are you apart and may never see each other again?

The first line of your post says it all.

She likes you but does not want a relationship,if you can accept this you will feel better and be able to concentrate on making other friends.

She did not say,no way,only that she is not interested in a relationship,writing a letter or telling her how you feel may back fire and you may end up embarresed.

She isn't ready for what you want, so back away, and get to know her better, and realize its friends only.