I've lost friends before. Not to death, thank God, but via the tidal wave that is time. Some friends I naturally grew apart from, some friends left me, very few friends I fell out with. Each friend that I've lost I still love in the time before we stopped knowing each other well. My love for old friends is frozen in time, it can't continue or grow, it just stays still like smiles in a picture. My friendships are probably captured forever as just that; smiling and frozen. A relic, to someone, one day. Or nothing but something to me.
Lost friendships are always sad. I mourn lost friends still even if it was good for the relationship to end. Friends, more than lovers, feel like they should last forever. But I know that that's not true now. Some friendships I have I know will last forever, others I know will be swept away by time. I feel sad even for those that haven't gone yet. As if I anticipate myself remembering my time with that person, or that group of people, and mourning a lost thing.
It's okay to lose friends. It's natural and normal. It is always just terribly sad.