Why isn't Yu Chengen Mulan together?

The reason why Mulan in Yu Chengen didn't stay together was that Yu Chengen chose to become a monk, and Mulan ended up with Li Liang. Yu Chengen felt guilty for killing his father, so he hit the tombstone with his head and was seen by Li Liang and Mulan. Li Liang and Mulan told Cheng En that the army needed him and wanted him to go back. Finally, because life was too painful, Yu Chengen chose to become a monk, and Mulan and Li Liang came together.