I'm always feeling the need of constant attention from my friend and I don't understand why.
Are you sure there's nothing that's behind this?
I don't like the feeling of being neglected if I don't get that attention.
I know you feel neglected, but you need to understand that your friend cannot give you all the attention you need. You have to realize that people have boundaries and we shouldn't cross them. You should focus on developing some independence.
I am perfectly independent. But I still need to know what my friends are doing. I can't do that if they don't give me attention. I need constant attention, or else I feel left out and hurt.
I understand wanting the be in the know about what your friends are up to and such. But people need their privacy and space sometimes and you shouldn't be so obsessive over what they're doing in their free time. I highly recommend you focus your mind elsewhere so it doesn't bother you as much.