I feel like I don't have any meaning
I'm sorry you feel that way. Are there others that have the same feelings you do?
Yes, but most people can't admit that to themselves.
You need to cheer up a bit, while being pessimistic is okay sometimes, all the time is not good. Your mental health means a lot, and you should take effort in fixing it so you can look to brighter days.
Don't tell me not to be pessimistic. I am happy being like this.
I'm sure you don't like feeling that way all the time. It's wrong to feel like you don't mean anything. You won't be able to keep friends if you are pessimistic all the time.