Keep in mind that I haven't read the manga. Thank you.

The events of the drama:
- Two high-school boys (cousins) move in to an apartment in the same building where the heroine (lets call her Yoyo) resides. One is cheerful/friendly (lets call him Smiley), and the other is Grumpy (lets call him that).
- So the Yoyo starts liking Smiley and confesses her feelings to him. But Smiley tells her that he doesn't believe in love and breaks her heart.
- Yoyo gets all sad/weepy whenever she sees Smiley. Grumpy jumps in and comfort Yoyo by telling her that he likes her and she should become his girlfriend. After a couple of therapeutic sessions (aka kind words from Grumpy + a hair-pin gift she receives from him), she starts to fall for him and they become a couple.
- However, Grumpy's ex-girlfriend appears and he starts going out with her because -in his words, not mine- "she is weak" and needs him. So he tells Yoyo that he loves her but he still has feelings for his ex. Therefore, he breaks-up with Yoyo to sort out his feelings for his (older + has a boyfriend) ex.
- Smiley takes this chance to jump back into the game! He comforts Yoyo and confesses that after he turned her down, he realized he loved her. *ehem*
- Yoyo gets all confused and sad/weepy again. This time she tells Smiley that she still likes Grumpy but will try to get over him by dating Smiley.
- Grumpy confront his ex: "who are we kidding? you love your boyfriend, so go be with him! We both need to be with who we want to be with!" Yeah, they break-up and Grumpy (the stone-head) doesn't realize that Yoyo is going out with Smiley to forget him, so he doesn't tell anyone that he broke-up with his ex.
- Time goes by and Grumpy tells Yoyo that he still loves her and that his ex is history. Smiley spots them very close to each other and runs to hit Grumpy on the face. Yoyo tells him to stop! Smiley goes away all grumpy.
- Anyways, now both guys want Yoyo and she can't decide which one she likes because she doesn't want to lose one of them. But then Sad-Smiley tells her that he hates himself when he is with her because of all the jealousy he feels when she is with Grumpy. So he breaks up with her.
- Grumpy tries to win her back but Yoyo won't make a damn decision. Then Smiley tells her that his grandfather wants one of them (him or Grumpy) to travel and take over the family business, so whoever she wants will stay.
- Yoyo can't do it! She can't lose them! Smiley says he will go but Grumpy decides to be noble and leave because he realized that she likes Smiley more.
- In the end Yoyo is happy because she didn't lose both guys! yay! WHAT?!!!

Comment:
Yoyo is a very disappointing character. She should have moved on when from the first time both guys broke it off with her. To be honest, both Grumpy and Smiley are not that great anyways. Okay, both of them helped her when she needed to find someone to adopt a dog (she found) but that's it. There was no depth in her relationship and no real talk about family and life with both guys. Perfect for increasing blood pressure.