@girlbandgeek I would say second rather than side - major secondary roles not just side characters.
I dropped Hometown, so don't know the couple you mention, but in the Drama I just finished there was the excellent STP that I mentioned AND a romance between a side pairing. The latter got minimal screen time and In the cast list at mydramalist they are listed as supporting roiles.
The STP in contrast was given a lot screentime, and the two characters are both listed as "Main Role" at MDL
@girlbandgeek Here are few of my favourite "Strong STP" #KDrama recs.
Miss Korea
Reply 1994
Lie To Me
Brewing Love
and here's a full list of all the East Asian Dramas I've watched, in case you're looking for ideas. Personal taste is VERY subjective ofc, but if you find one or two here that interest and/or appeal, that would be lovely.
https://docs.google.com/spreadsheets/d/1XTBrjR-blgIJf2IcCbZPYzH4zqhb1XDL0NLwpUwOpCI/edit?usp=sharing