The song is partly in Chinese and partly in Korean 
Did you guess it it is sung by the two lead 

The Myth 

Endless Love

(Male)
Free me my most secretive await
The stars are falling the wind is blowing
Finally, I can hold you into my embrace again 
Both hearts are trembling

Believe me my unchanged true heart
Thousand years of wait contains my promise
No matter how many cold winters have passed
I will never let go of my hands

(Female)
Hold tight my hands now close your eyes
Please remember those old days of our love
Because we love each other so much
That is why we feel even more painful

We can't even utter the line "love you"

(Male)
Every night pierced by painful heart
My longing never ends
I have long got used to the company of loneliness
I face it with smiles

Believe me you have chosen to wait
No matter how much pain ... you will not shunt
Only your gentleness can free
the borderless indifference

(Female)
Hold tight my hands now close your eyes
Please remember those old days of our love
Because we love each other so much
That is why we feel even more painful

We can't even utter the line "love you"

(Together)
Let love be ... in our heart ...
the flower that blooms forever ...
Transcending time, we will not bow to defeat ... the dreams that we won't give up ...

(Female)
Because we love each other so much
That is why we feel even more painful

We can't even utter the line "love you"

(Together)
Let love be ... in our heart ...
the flower that blooms forever ...
We shall never forget ... our mutual promise

Only true love will accompany you and I 
Transcending time and space

(Female)
We can't even utter the line "love you"

(Male)
Love is the only beautiful myth that has never changed in my heart