It features guest vocals by American rapper Puff Daddy, who also co-wrote the song with Aion Clarke, Michael Jones, Leroy Watson and the producer Mario Winans.

It was well received by music critics, who complimented its minimalist style recalling Bad Boy Records' classic hit singles of the 1990s.

The song's accompanying music video was directed by Bernard Gourley and features Cassie and Puff Daddy in different sides of a wall from adjacent apartments while performing the record to each other.

Cassie appreciated the treatment had a "nice story" that wasn't overdone which she felt added warmth to it allowing Diddy to have a bigger role in the visuals.

"[3] The album was then scheduled for a spring 2009 release and Cassie talked about its production and mentioned other collaborators also included Pharrell Williams, Darkchild, Kanye West, Ryan Leslie, Bryan-Michael Cox, and Mario Winans.

Diddy confirmed on his video blog that her new album would be called Electro Love and was slated to be released later that year, with Cassie telling MTV News: "You're definitely going to see more independence [...] a difference in vocals, a little bit more personality.

"[14] Bill Lamb of About.com called Cassie the "queen of minimalist soul" and remarked "Must Be Love" to be almost as "effortlessly catchy" as her debut single "Me & U."

"[15] According to a writer for Rap-Up, the song recalls "Bad Boy circa the '90s,"[7] and, at MTV, it was referred to as a "minimal R&B slow-burner with a beat that sounds like rain" and that "[Diddy's] rhymes definitely beef up the track.

"[16] Tom Lea of Local Action Records stated the song is "pure heartbreak" and praised Cassie's vocal performance, adding: "if the "I think about you all the time" line doesn't make you melt on sight, you've been on the internet too long.

[32] It was also sampled by Snakehips on their version titled "Miss U Always,"[33] and by producer Rupert Taylor, otherwise known as xxxy, on "I Know This Can't Be Love," from his 2012 Everything EP.

In the Gourley-directed visuals, Cassie and Puff Daddy are shown in two separate apartments performing the song to each other through opposite sides of a single wall.

In the treatment, the director describes the video concept as "something smoldering and sensual [...] cinematic [...] dripping with desire," set in the middle of a heat wave established with a series of detail shots, creating an intense mood with dramatic lighting.

The 2002 wuxia film Hero and Gordon Parks' photographs are used as reference to form this tension while telling the story of "an extraordinarily hot day inside the two adjoining apartments," as the increasing heat throughout "becomes a metaphor for love."

The focus of the video are Cassie and Puff Daddy's performances in a "simple but dramatic" setting as they "internalize the desire" verbalized in the song's lyrics, accentuated by the wall separating them which is brought to its combustion point, reaching a climactic moment when smoke and flames start to build around them.

"[13] Rap-Up wrote that the video featured the "most-talked-about haircut on the Internet," after Cassie created buzz with a new look when she shaved the right side of her head a couple of months prior to its release.