Well, try these:
Shinjae - Tears are fallin
B1A4 (Sandeul solo) - Crush
Hyuna ft Junhyung & G.NA - A Bitter Day
JYJ - In Heaven
K.Will - Love You
B2ST - On Rainy Days
Davichi - Be Warmed
Davichi - I Made An Accident
Davichi - Dont Say Goodby
BTS - So 4 More (well, thats work for hopeless adult like me -_-" )

Blossom tears-Lyn ft. Leo
Look up Davichi MV videos or maybe Huh Gak videos they are mostly ballad and some MVs have a sad plot

Im not sure about crying big here are some I find to hit a nerve.
Please Don't-K.will
Gone-Jin
Without You- Lee Michelle