"Understand that friends come and go, but for the precious few you should hold on. Work hard to bridge the gaps in geography and lifestyle because the older you get the more you need the people you knew when you were young" — Mary Schmich
Family are forever. You can keep them, lose them, find them again and while we all pass in the end they won't be forgotten even when they are gone. Unless you want them to be forgotten, in which case you are lucky if you succeed.
Friends can be like family and rarely forever. The best friends are family in which case you can build your own from your best friends. Always handy if your own biological family isn't to your liking, or around anymore. However they suffer from the same longevity issues of family.
Files should be forever, but rarely are. They get lost, deleted, archived and forgotten. Software that was used to create them is lost, unmaintained or doesn't run anymore on your operating system. Compatibility is a huge issue as new software is created to replace old applications. If you really want to keep it forever, print it on acid free paper and file it somewhere dark. In the meantime make a PDF until we work out some other forward compatible file format that will last forever. Make backups and then make backups or the backups.
Photos do seem to last forever, or at least a very long time. Printed photos get damaged, creased, torn and depending on the technology of the time fade. Evidence would suggest in their printed form they last a long time - say 200+ years - and in digital form conceivably could forever - although see above. Physical photos can be converted into digital photos and we don't have too many image file formats to contend with forward compatibility yet.
Diamonds are forever, well at least according to Dame Shirley Bassey.