The Baker on the First Floor
I think it would have liked it more if the whole story focused on the main couple and their struggle to face their past and understand (and make the other understand) that they love each other for who they are despite resembling each other's past lovers. This idea, if given enough context and if explored thoroughly in terms of emotional insights, would have made a great story as it was, but the author actually tried to fit in it a lot of different themes and even tried giving every single character a story of it's own in less than 70 chapters, so it's only obvious that it lacks depth more times than not. Instead of coming up with a new story for every secondary character, it would have been better to provide a better explanation for the reasons they acted the way they did in the past (in other words, to give us a more definite picture of their personalities). To me it was often confusing, I always felt like the author was giving some things for granted but never took the time actually express them clearly, so you kinda always have to trust what the characters say they perceived to make the story make sense, you're not given enough material to understand and judge things on your own.
Soshite Boku wa Koi wo Shiru