"Bittersweet" is a down-tempo R&B song which also derives from soul music. According to Margaret Wappler of The Los Angeles Times, its introduction is composed of "anguished" piano notes and "gut-socking" moans. The song lyrically sees its protagonist reminiscing on a past love.
Margaret Wappler of The Los Angeles Times said Fantasia's best moment on Back to Me was "Bittersweet", stating that it was "smartly chosen as the album’s first single." Mikael Wood of Entertainment Weekly recommended the song as a download from the album, calling it a "old-school slow jam." On songs such as "Bittersweet", Mariel Concepcion of Billboard said "her distinct voice is most enjoyable when singing heartfelt ballads." Jonathan Keefe of Slant Magazine was less enthusiastic of the song, commenting that it "barely has a melodic line" and that it "just lets Fantasia do what she can with its bathetic series of clichés."
The music video for Bittersweet has been shot and premiered Friday June 25 on Vevo. The video was directed by Lenny Bass and features professional football player Devin Thomas as Fantasia's love interest.