While I admire ur courage in telling her u like her, I wonder if
u have thought of why you two are not together despite knowing each
other for so many years liao? The thing is, some girls will never
consider their guy pals/buddies to be their boyfriends because they
know everything about the other person already. She telling u its
too sudden means that she has never thought of u in a romantic way
before.
But then again, she telling u "She need time to think about it"
means u still have a chance, as compared to she rejecting u
outright. Your story seems to be a little similar as my, and as I
know I can never be with the girl I like for 10+ years, I wish u
success. Tell us the answer, k?