I suppore it has been said already that depression is a disease that makes you confused and makes you feel like cxap. And that is not your fault.

I said it again because it can never be repeated too much.

But also, depression makes you a horrible friend. A person with depression is unpleasant because he/she is depressive. If you care, it is frustrating because you can't make him/her feel better.
One can only overcome and tolerate this situation if he/she understands how depression works, and if he/she loves you. At this point it is clear how DISADVANTAGED a depressed person is in being appreciated. The fact that you do have friends (and they must be true friends!) demonstrates that you are a particularly GOOD friend

The best of luck