How do I stop feeling jealous and abandoned by my sister?

I feel like she is going to have a great career and relationship and forget all about me. In the past we were really close and could talk about anything. Now I feel like she could care less about me. I have always tried to be there for her, so I don't get it.

Whenever I think about my life it feels like a dark pit of depression with no hope in sight. It's getting so bad that I will probability be going on disability soon. Now I also feel like I've lost my closest friend:(