Kdrama were the 2nd male and female lead have good romance between them

I want dramas were the second main characters have separate love line and both of them focus on themselves rather than mingling with the main characters. 

Something like 'oh my venus' is what I'm looking for, were the 2nd lead first liked the female lead but starts to like the 2nd female lead and was really serious with her and the 2nd female lead already liked him, so this is something that I'm looking for, something like this only.

They should have a happy ending and a genuine amount of development through the drama. Mention the couple and drama please. 

Don't tell me dramas with crazy mother's in them.

 AH:

High Society - Yoo Chang Soo and Lee Ji Yi stole the show at times.

Watched it

when i read this first drama which came to my mind is DOTS and Goblin!!! so for now these are the one i remember!!!

Descendants-of-the-sun (Yoo Shi Jin & Dr. Kang Mo Yeon (Main Couple), Seo Dae Yeong & Yoon Myung Ju (Second Couple)

Faith  (Doctor Yoo Eun Soo & General Choi Yeong (Main Couple), King Gong Min &Princess Noh Goog (Second Couple)

Goblin (Kim Shin / Goblin & Ji Eun Tak (Main Couple), Grim Reaper & Sunny (Second Couple)

Fight-for-my-way  (Ko Dong Man & Choi Ae Ra (Main Couple), Kim Joo Man & Baek Seol Hee (Second Couple)

Arang-and-the-magistrate (Kim Eun Oh &Arang / Lee Seo Rim (Main Couple), Dol Soe &  Bang Wool (Second Couple)

Heartstrings (Lee Kyu Won & Lee Shin (Maincouple), Jong Yoon Soo & Kim Suk Hyun (Second Couple) in this in the beginning Shin has a crush in Yoon Soo but later it is solved since she is a professor)