The song "Baby" by Clean Bandit & MARINA (featuring Luis Fonsi) explores the theme of unrequited love and longing for a past romantic connection. The lyrics depict a person who is reflecting on a previous relationship and the regret they feel for letting that person go.

In the verses, the narrator reminisces about a past September, symbolizing a time of nostalgia and fond memories. They acknowledge their youthful ignorance about love and admit to being captivated by their former partner's wild and exciting nature. However, the narrator also reveals that they gave their heart to someone else, expressing remorse for their decision.

The pre-chorus reveals a sense of resignation and acceptance that they missed their last chance with their desired love interest. Despite the pain, they acknowledge that it's time to move on. The chorus, "I'm already someone else's," emphasizes their current unavailability and the fact that they cannot be with the person they still desire.

The second verse portrays the narrator's struggle to resist the temptation of rekindling the past. They express the intense connection they still feel when their hands are near each other and the difficulty of not hearing the words they long for. They suggest leaving things as they are, cherishing the memory of their former partner like a lullaby.

The third verse, performed by Luis Fonsi, adds another layer to the narrative. He affirms that despite the person's claims and attempts to remain friends, he knows they still have feelings for each other. He expresses deep devotion and obsession, claiming that he will always belong to them.

The chorus is repeated, emphasizing the narrator's longing and realization that the love story between them and their desired partner has come to an end. The lyrics suggest that they both feel the same way but are unable to be together. They acknowledge that the person deserving of their desired partner deserves better and that what they have with their current partner is not true love.

In the final lines, the narrator expresses the pain of missing their desired partner every night and the realization that their feelings go beyond friendship. The countdown at the end signifies an impending separation and the urgency to confess their true emotions before time runs out.