Why Fionna's actions this episode make sense

Not to excuse her behaviour at all, but, narratively, it makes sense for her character to crash out like this. She:

• has been working to fund raise for her friends when she can't even pay rent and was evicted

• is suffering with PTSD flashbacks of the Winter King dying when she kissed him (don't forget he died because she kissed him, as the crown was keeping him alive and she had that thing where stuff she touches lose their magic)

• witnessed Finn die numerous times and failing to save him all those

• witnessed people she knew from Vampireworld die (when she was in Finn's dream, Finn's dead body glitched to Martin's from Vampireworld, so that is clearly affecting her)

• killed all those Candy people in Winter King's world, when they appeared as monsters. Then found out they were innocent victims of the Winter King (and she specifically comments on how she feels bad about that in the next episode)

• witnessed Jerryworld BMO brutally die

All the while she's been told she is a copy of this amazing hero, and she too used to be an awesome hero. I can see why she crashed out. Her life kind of sucks, she's suffering with a ton of trauma, and it seems the only thing she was attaching her worth to was saving the Sweet Spot (and DJ Flame still being into her). The Sweet Spot being saved without her made her feel worthless, like she really isn't a hero and has nothing that gives her purpose.