I found an interesting article about friendship at http://www.the-river.org/resources/messages/2000/000319keith.html.
If friendship is forced or manipulated, it ceases to be a friendship - the joy leaves and it becomes a burden. Real friendship is love, and love must be given freely or it is not love.
Real friendships can't be forced. They must be chosen, and then pursued and purged of ulterior motives. Friends share secrets, and understanding of each other grows - so does trust and appreciation. If the friendship deepens, one day you wake up and realize that you love your friend for who they are, not for what they can do for you. In fact, they don't need to do anything for you. Just being with your friend is the highest joy. Yet the truth is that there is nothing you wouldn't do for your friend and nothing your friend wouldn't do for you.
I also found this article on emotional dependency. It's painful to read, but not in a judgmental way.