The duet speaks on the infinite but tragic love in between Chang'e and Houyi, who're based upon the Chinese fantasy of the moon goddess, upon which the film is based on. Amongst many artists that have recorded variations of "Always and Forever" is definitely the American R&B vocal team Whistle, https://always-and-forever62616.angelinsblog.com/36172026/always-and-forever-mine-for-dummies