"
Amureohji anha
Hamyeo nal jisbalpa
Utneun eolgureul boni da ijeotna bwa
"And just like that
You broke my heart
Your smiling face shows that you've moved on"
He's saying that their relationship ended just like that and suddenly she found someone new and is smiling and happy with them, while he still thinks about her.
The emotions in the song are quite spiteful.