Is it normal that i've never cried since i was 8?

You didn't specify how old you are now.
If you are 9 now, then it is normal.

You are missing out on one of the great releases in life. It is not only not normal, but unhealthy to prevent yourself from crying, on occasion.

Just cries, but Just hides his tears in rain.

Just not does cry! Indeed.

Words.

accidentally slip on a knife -_-

No, it isn't normal. Crying is a normal, healthy part of life and it's important that people do it once in a while. Otherwise, all of that emotion gets bottled up and it results in compromised mental and emotional well-being.

I cry very easily - when I hear a sad song, when I see babies laughing, a film, a book, my thoughts. I am very sensitive. I can't understand.

Sometimes I just need a good cry. I'm sure some girls will understand what I mean :P :/

I have a problem of not crying enough, but 8 is really young!