Where Have All the Flowers Gone(2002)

Gao Ju (Xia Yu) and Zhang Yang (Pu Shu) were best of friends, but they fall in love with Huanzi (Zhou Xun). Huanzi loves both of them and thus they formed an unbalanced trinity. A simple promise not to meet ever again after college ended up in disaster when Gao cannot resist wooing Huanzi again