I loved it.
It was very realistic even though it had the unrealistic part with the magical notebook.

You have to realize the main part of the girl's journey to understand why she is behaving the way she is - the thing most people who are disliking this apparently overlooked - that she grew up horribly unloved. One parent died early, the second one therefore shut down and stopped acknowledging her entire existence. More to that, the rest of the family blatantly blamed her for the whole tragedy so she had NOONE, I repeat NOONE who would give her even the littlest of love, since she was a small CHILD.

So the fact she's using the notebook over and over again is absolutely true to her character.
Is it wrong? Well, she does not force the guys to date her forever against their wishes, they are free to leave her once the month mark is over and they usually do. It's not right thing to do, yes. However she understands it's not real, it's temporary bandaid to her loneliness and absolute thirst for someone making her worth and classically not realizing that the most important person who has been loving her ever since and could give her everything she wants, is right there, in front of her.
In conclusion, FL is not picture perfect.
SHE IS FLAWED. And I think she kinda knows it, but she's just scarred and exhausted from carrying everything on her back, alone, all her life.

I even think we might all know that one person in real life who thinks that being in a relationship is just the must that will solve all the problems.

Again I loved it as it was very real.
And Do Young's character Si Ho was also behaving kinda unsuprisingly, trying to get out of the unrequited love column but still knowing he won't succeed as he's deep down in the love zone for her and he's give up on moving on and just live in the shadows.
That's the most unrealistic part of this, I wish each and every one of us had such a gentleman/white knight guarding us!

I haven't seen the ending episode yet but had to write this so it is not flooded only with not so positive reviews.

The actors did a great job, especially Do Young and his panic attacks.
If you're looking for a fluffy lighthearted romance, this is not it.
It's heartbreaking but realistic.