Welcome to PC. This is what we do. We listen and try to give support. It's really hard for most people to understand depression. Your Dad either doesn't know how you really feel or doesn't know how to cope with it. He's probably not blowing you off. He just doesn't know what to do.
You do need to talk to someone and get help. You are carrying a lot of weight with your best friend depending on you as she does. It's encouraging that helping her makes you feel better. Helping others is such a positive way to feel that feeling of purpose and worth. That said, you must not feel that it's up to you to fix her. You can care and talk and be there, but she needs to see someone trained to deal with problems as profound as hers. It's just too much for you.
I hope you find some help soon. Post here as often as you need to. We're ready to listen.