Is it normal i feel sad when fictional characters get older

I was reading a book where it starts out with the main character being 10 years old and he is friends with a girl the same age, but then his family moved away and he only tries to contact her again because he likes her and only sees her again at the end of the book, but 30 years has passed in between. At the end they both talk about how they wee friends as kids and had great experiences, and at the end they're both in their 40s and she is poor but has a big family with lots of children and she and her husband barely get by but she is happy, while the guy is rich but depressed, single, and bitter about life. The whole story made me nostalgic and sad that these fictional characters had to age and couldn't stay kids forever, and also that they never got together. For example at the end of the book he reveals that he always had feelings for her and she says that she felt the same way about him, and they were soul mates but they never got into a relationship together. It just makes me so sad.