The two have been together for about five years, and publicized their relationship back in 2015.
After they went public, Cho Jung Seok and GUMMY have numerously shown their love for each other.

Although GUMMY is quite shy about mentioning Cho Jung Seok on television, that does not seem to be the case for Cho Jung Seok.
There were many times when Cho Jung Seok has publicly shown his love for GUMMY.
It is time to take yourself back in time to look back at these moments!
1. Cho Jung Seok always mentioned GUMMY when accepting an award
During the acceptance speech at different awards ceremonies, he never forgot to thank GUMMY.
For instance, after winning the grand prize at 'MBC Acting Awards' last year, Cho Jung Seok said, "I also would like to thank GUMMY, the person I dearly love."

In 2016 when GUMMY appeared on MBC's variety show 'I Live Alone' with singer Lena Park, Lena Park became annoyed at GUMMY for speaking to Cho Jung Seok on the phone again.
GUMMY later commented with a smile, "We are used to people reacting like that now."
Her statement showed how frequently they talk to each other on the phone.

Cho Jung Seok and GUMMY composed one of the tracks titled 'Shall I go?' (literal translation) in GUMMY's fifth album together.
The album was released in June 2017, and Cho Jung Seok has apparently played guitar during the recording of the song as well.

GUMMY previously mentioned that they both frequently monitor each other's activities, and Cho Jung Seok gives her some useful feedback.

There were times when the couple's breakup rumors arose in the past.
Whenever this happened, Cho Jung Seok had always quickly denied the rumors before GUMMY got hurt by them.

(SBS Star)