4 days ago, Olivia Olson confirmed that Marceline and Bonnibel have dated before. The reason it has been confirmed is because the new Adventure Time book coming out soon may have details on their relationship, and their relationship obviously can’t be aired on TV because some states of America (and countries in the world) are against same-sex marriage and relationships.
But yeah, they have indeed dated before.
Can we also talk about official Bubbline art drawn by Natasha Allgeri, former character designer and story board artist for Adventure Time, and now Showrunner of Bee and Puppy Cat!?