Songfacts®:

• Here, Machine Gun Kelly ruminates about a messy entanglement involving his former girlfriend's best friend.
  
  I swear to God, I never fall in love
  Then you showed up and I can't get enough of it
  
  Instead of wallowing in misery following his breakup, MGK has rediscovered love. However, the rebound relationship with his ex-lover's right-hand woman creates complications.
• Blackbear joins MGK on the track. During his verse, he addresses his ex, outlining the problems arising from the end of their romance. He has moved on, and wants her to stop contacting him and do the same.
• Machine Gun Kelly's first four studio albums all featured a hip-hop style, but following the release in 2019 of "I Think I'm Okay," his rock-leaning collaboration with blink-182 drummer Travis Barker, the Ohio artist wished to explore the sound further. After Kelly recorded the pop-punk song "Bloody Valentine" with Barker, the pair agreed to collaborate on an entire studio album with Barker on drums and as a producer. "My Ex's Best Friend" is the third single from the project.
• Kelly, Blackbear and Travis Barker wrote the song with Nick Long, who is a member of the American indie-pop band Dark Waves. Long's other credits include All Time Low's "Dirty Laundry" and Bebe Rexha's "Last Hurrah."
• Kelly performed this song with Blackbear and Travis Barker at the 2020 VMAs pre-show as one half of a medley along with "Bloody Valentine."
• The Van Alpert-directed music video shows MGK jamming on the guitar as Blackbear tows them through the desert. Actor and director Van Alpert's other credits include the clips for Post Malone's "White Iverson" and Local Natives' "When Am I Gonna Lose You."
• Machine Gun Kelly performed this song on the January 30, 2021 episode of Saturday Night Live. It marked his debut appearance as the comedy show's musical guest.