You said she doesn’t want to be your partner, but she’s a good friend. So maybe you need to re-define this relationship as good friends only. You mention that you tend to think in black and white terms. You also say you have a tendency to snowball things into much more than they actually are – that’s called catastrophizing. Both these patterns of thinking may be resulting in you interpreting this relationship in a distorted way. Could that be?
A shared meaning in life is a deep connection to your partner, reflected in a shared passion or life dream. It’s the kind of thing shared in marriage vows. Have you considered seeking professional counseling, face to face, to help you process your feelings? If you have depression, it’s important to seek treatment before it gets worse. It sounds like dealing with rejection is a main problem for you. Maybe you need to work a bit on the most important relationship of all – the one with your inner self.