I think I understand what you're feeling. For a long time I looked to fill up the emptiness inside me with other people. I wanted so much more from my parents than they would or could give, from my brother too. I was the same with friends. Eventually, the emptiness grew to a point where I started drinking. I think the bottom line is that you have to learn to love yourself first and foremost. What others think about you doesn't matter. I am very sorry that your sister has cancer and that you will lose the sister relationship, but you are strong enough to shine brightly on your own without your family's approval.