I think people are clingy when they look for someone else to make them feel good and who dont have a good sense of self worth so they try to get as close as possible to someone they supposedly "love" because they love the feeling it causes. When people want to experience a "symbiosis" with their partner and dont want to realise that no matter how much love and how close you will always be 2 people with 2 different experiences...
I think making sure you learn to be happy with yourself and love yourself will avoid you being to clingy and dependent on someone else. Its only when you love yourself someone else can truly love you. Everything else is just a selfish attempt to find someone else who can make you feel ok....thats understandable but its not love.