I'm not mad because of the sad ending, I'm mad at how they ended the beautiful relationship ridiculously, the tunnel scene was well written but things after that happened ruined the atmosphere. the photo on the album is never explained. I'm not the person who hates open endings, but if you show smth on previous episodes at least you should explain part of them. I think the writer cut corner through the use of a lot of nostalgic scenes for the final episode. this sounds lazy to me.
7,8,9 and 10: 9/10
11 and 12: 5/10