I feel like I'm worthless again because my best friend cut me off
What is making you feel worthless again?
Because he has so much potential and I suck
I understand, but it's not good to base your self-worth on others. You should learn to love yourself for who you are.
He should appreciate me more.
Because he has potential? It's not his fault that things are going well for him. You should be happy for him instead of seeking appreciation for nothing.