Depression can be especially cruel in that it doesn't affect just the depressed person, but everyone around them, too. Someone who is depressed can be very difficult and draining to deal with. What makes this so cruel is, that as a depressed person's relationships become strained--to the point where others actively avoid having anything to do with them. This further contributes to a worsening self-image and makes the person feel even more isolated, intensifying the depression.
(If you're getting the idea that depression is an exceedingly heinous illness, preventing those it afflicts from finding treatment, and plunging them into ever-deeper isolation, then you understand just how horrid this illness is. No other disease, physical or mental, reinforces and feeds itself, as depression does.)
Depressed patients must learn to understand how their illness affects other people, and expect that their relationships will not be what they were, for some time. By the same token, those around them must understand that it is not the person, but the illness, which is an inconvenience. The best way for them to be relieved of the stress, is to help the patient toward recovery. This means getting the person into treatment, if he or she isn't already, and remaining supportive--no matter how difficult that may be. (Often the depression causes patients to drive others away, so this can be very daunting, indeed.)
Friends and family must remember that the depression patient did not ask for this illness, it is not a character flaw, and the patient often doesn't have much control over what he or she does. They cannot afford to take the symptoms of depression in someone else, personally.