Why do i have feeling of being depressed with the knowledge i'm not important to anyone?

Supportive therapy: Of course that feels awful. But, "know" may be too strong. Try "believe". A rational-emotive therapist may help avoid the traps that can make things even more painful then they need be. If you can get through this, you might find other people to build value with. If you are religious, a counselor of your faith might be a place to get in touch with your true worth. Don't give up or be too picky.

Painful: This is certainly painful, but can also be an over-reaction. If not, it may speak to your own difficulty extending yourself out to others in an unselfish way. Many depressed people are in this mode, and need help in normalizing their relationships with others. A psychologist can help you with either of thes possibiliies, if you are willing. Be well.