"I'm Just Your Problem" is a song featured in the episode "What Was Missing." The song is written by Rebecca Sugar, produced by Tim Kiefer, and sung by Olivia Olson (Marceline's voice actress), backed up by Finn (beatboxing), Princess Bubblegum (synthesizer), and Jake (viola).
The song seems to be about Marceline's anger with Princess Bubblegum; the middle lines raise questions about her true feelings.
It implies that her desire to reconcile and her frustrations are genuine.