I have the same issue. I get attached to many people. I was never the popular kid, and was abandoned many times in life. Physical, emotional and substance abuse have been problems in my past. I feel alone much of the time, even in the presence of many. As I grow older I am beginning to see that people come and people go and it will always make us feel sad or abandoned, its who we are. We just have to begin to believe in ourselves more and begin to understand that we are ok alone, we are going to survive. Its alright to miss someone and cry over someone leaving as long as we can pick our head up and know we can carry on. You have to find some self-worth and life-worth that will help you grow stronger as a individual. In order to have strong partnerships we have to know that we are strong, love-worthy, secure individuals. This takes work. Buy the book "Healing the Shame that Binds you," By John Bradshaw and the book "Notes to myself." These books have helped me a lot. Don't be afraid of human relationships. Interacting with others and loving others are two aspects of life we must experience in order to be healthy. When people leave tell them goodbye and you're going to miss them but know that you will be ok and that they will be ok, your both going to survive and live long happy lives.