It can be very painful and depressing when you see others who have what you want. Seeing what others are experiencing can make us aware of what we do not have. This life can be very devastating and sometimes our thoughts can comfort us but at the same time torture us.
I'm not sure I feel much nostalgia at all towards anything, because I know that I would still want to die no matter the situation I was in, but sometimes I do view the past as being better than it actually was, just because I feel distant from it now.