This is one of Fleetwood Mac's best known songs, and as one with a Christine McVie lead vocal (she wrote the song as well), you know there's a story.
Christine was married to John McVie, the bassist (and frankly the Mac) in the band. In 1975, their marriage was on the rocks, and she was feeling troubled. So she wrote a very happy-sounding, sweet-sounding song that was basically begging her husband to tell her that he loved her.
Which might be why she absolutely doesn't look like she's having fun performing the song.
The song didn't work. They divorced in 1976. Nevertheless, she stayed with the band until 1998.... their Rock and Roll Hall of Fame induction. She still didn't look like she enjoyed performing the song (although Lindsey Buckingham sure was enjoying the banjo). One other noteworthy aspect of this performance: John McVie is singing backup vocals.
Christine rejoined the band in 2014. She finally looks like she enjoys her cheerful little ditty.