Seeking the title of a song is a beautiful and happy song that is repeatedly sung in Korean songs. What's its name?

Tell me your love! Jang Keun Suk and Wen Genying played the opening song of Romantic Mary, which was not sung by Jang Keun Suk. It seems to be: Oh I love you, love you, love you forever ~ Oh I love you, love you, love you forever ... Supplement: Really? I happen to have this song in my mobile phone.