When I was in high school, my best friend and I shared a journal. Each day one of us would take it home, write in it, and reply to the previous message. The next day we would hand it over and the other would repeat the process. My friend (who is two years older) took it with her to university after she graduated. It was a great record of our friendship.
My sister and I did a similar thing a few years ago, but in separate books. We each wrote a journal about our fondest memories of each other growing up, then gave the books to each other as a keepsake. My sister’s journal to me is one of my most cherished possessions and contains many happy memories.
I’ve read about famous couples who kept joint journals. For example Charles Darwin and his wife Emma kept a joint journal about their children. Mary and Percy Shelley wrote a journal together about eloping to Europe, which they later published as a travel journal.
Have you ever kept a journal with someone else?