So hear me out. The start & end of this story will come full circle. It starts with them reminiscing happy memories together and ending with it
In episode 1, we see the drama start in the middle of their love story (their marriage) and the finale, will end at the beginning of their love story.
BUT Hae-in might have memory problems/ completely forget and Hyun Woo is by her side to make her remember. That's what the 10th-year message video is for. (A time jump maybe?)
Also, THE BOOK they were reading at the bench park, called "Singen und Sagen, a collection of German ballads" means singing and saying.
I think this book is one of the inspirations of the story. It's about love, loss, magic, and human nature. They resonate across time, exploring the depths of the human experience through lyrical storytelling. There is a difference between saying a story and singing it. You remember a story even more when you sing about it because you know it by heart.
The characters' relationship storyline combined with OST is so beautifully done in this drama.
All to say, YES we will have a happy ending but a bittersweet one.