Understand meaning of lyrics

Yesterday some guest came to our cafe in the afternoon.

So I was really glad.

In the evening, a student came to take Korean lesson, after that English conversation seminar was held at our cafe.

This time we sang 'Last Christmas'.

This song is very famous, but I have not known the mean of the lyrics until now.

Now I understood the mean of the lyrics, therefore from now on I'll have different feeling when I listen to this song.