i really love dramas with side couple along with main couple. these are the dramas that i have already watched.

boys over flowers- awesome side couple

perfect couple(c-drama)

just you(c-drama) there were many side couples in this

pretty li hui zhen( the side couple's romance was very nice)

legend of the blue sea

autumns concerto( well it kinda looked like the second male lead ended up with the girl who was his friend)

it can also be about two couples( as like in goblin) but they should end up together. so pls recommend me any drama with that kind.

Descendants of the Sun
A Gentleman's Dignity (3 side couples)
The Master's Sun
Reply 1988
Reply 1994
Reply 1997
Coffee Prince
Oh My Venus
Heart to Heart
My Wife’s Having an Affair this Week
It's Okay, That's Love
High Society(main couple is really annoying though)
Delightful Girl, Choon Hyang
High School King of Savvy
Witch's Romance
Cinderella & The Four Knights
Dream High
Innocent Man
Love O2O
Plus Nine Boys (3 couples if you include a 5 year old)
Weightlifting Fairy
Discovery of Romance
Sweet Stranger and Me
Arang and the Magistrate
Bachelor's Vegetable Store
Flower Boy Next Door
Legend of the Blue Sea
Love Rain
Mary Stayed Out All Night
Secret Garden
The Heirs
Warrior Baek Dong Soo
You're All Surrounded
The Lover
thanku so much every one for your suggestions 
There is also Can We Get Married, Madame Antoine, School 2017, Bride of Habeak, Age of Youth 1 and 2, Ode to Joy 1 and 2, Discovery of Love.
GOBLIN - to a point where you are more excited to see the side couple lol. It's one of the best imo.

Five Enough - only reason I kept watching was for Yun Tae and Sang Min, was literally skipping around just for these two.

Gentleman's Dignity - Main couple + 3 side couples that are also worth watching imo

King2Hearts - prepare your heart though