Good start but horrible plot development

This is one of the most disappointing dramas of 2020, it started with one of the best first episode I've seen in kdramas but I don't know what happened but it became so tedious. I don't know if I would see it again.
I have a love-hate relationship with this drama, it's one that I will miss (or maybe just the comment section) but I can't say I liked it, it had several plot holes and I don't think I can give it a high rating.
What I really loved about this drama was the ost, all the songs are beautiful. Let's not forget that they focused too much on the love triangle that business took a back seat.
I'll start to describe what I liked and didn't like about each character.
• Dosan: I think it is the worst ML I have seen in kdramas, he's selfish, immature and I will give reasons why I did not like the character.
1. He started a relationship with Dalmi by pretending to be the Dosan from the letters
2. Left Dalmi alone in the park while drunk.
3. When Dalmi asked you for space, what did he do? He followed her and faked chance encounters with her, and they made it look "romantic" when it's NOT.
4. I have listened to their private conversations.
5. He hit the HJP when he said nothing but the truth and then asked him for a favor using his weakness which is the grandma.
6. He didn't want to return the letters to HJP when they belong to him.
I can give many more reasons but this would be longer.
• Dalmi: I think it's the worst FL I've seen, at first her character was very good but as the episodes went by she had a setback it almost seemed like she always needed a man to help her when at first it was the opposite. A main part of the plot was the letters but it seems that she forgot about that and never asked HJP what happened or why he did it, instead he started dating Dosan and was indifferent to HJP.
• Han Jipyeong: I can say that he was the best character that the series had, he is a tough person at the beginning but he was almost the only character that really changed in the 3 years and he showed to be a very sweet person.
• Injae: I liked her character even though she didn't have much screen time she really changed and I really liked the ending she had. Her character gave for more.
• Yongsan and Cheolsan: Immature.
• Saha: His character contributed almost nothing and was not very memorable.
Now I will talk about couples:
• Dosan and Dalmi: I didn't feel they had chemistry and I don't see a future for their relationship, they started dating because Dosan pretended to be someone else, she's one of the worst couples I saw in dramas.
• Cheolsan and Saha: It was such a forced couple, they had no chemistry at all and Cheolsan being jealous when they had been dating for like 1 day (? Cringe
I want to add that Yongsan's brother's plot was VERY unnecessary.
The guys from Samsantech claim to be close friends but why didn't anyone know Dosan entered college early or about Yongsan's brother?
The reason I can't put a bad rating is because I loved HJP's character and Seonho's acting.
-English is not my first language so I apologize if I have any mistakes.

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