What causes someone to act needy?

@Miram But, how does being needy solve that feeling of being abandoned or the fear of it... or anything else?

@MarkPaul It doesn't. We don't feel neediness because it's a solution. It's a consequence. It's not a problem too unless you're acting too much on it and it affects other people.
I guess to work on it when it's a problem, you'll have to address the reason and learn to regulate it. You have to take responsibility and be ready to change.