They were children when they first met, but at that time they had no idea how important they would become to each other.

"Marceline! That's too distasteful!"
"Come on,Bonnie! I thought Princesses' were supposed to kiss their Knights." Marceline teased.
Bonnibel pouted while Peppermint Butler and the King of the Nightosphere looked on amused. Whenever the two girls played together Marceline always managed to bully herself into being the one that saved Bonnibel. Her reasoning being of course that, as the older one, she was sworn to protect 'her Princess'. Said Princess would usually just roll her eyes, but today she was in no mood for Marceline's behavior. In an act that was rather out of character for the usually mature young girl, Bonnibel stuck out her tongue and stomped off, Marceline hot on her heels shouting apologies.
"Do you think we should intervene?" Marceline's father asked looking a little worriedly after the girls.
Peppermint Butler thought it over a moment.
"They'll be fine."

As they grew older, their tastes began to change. Bonnibel took an interest in science while Marceline was more interested in playing guitar. Despite this they still cared for each other more than anything else in the world.

"I just can't believe he would do something like that!" Marceline cried. Bonnibel shushed her and stroked her head. "What kind of dad eats his daughter's fries?"

"It's not funny,Marceline!" The usually pink Princess shouted as she tried to brush soot out of her sticky hair.
"Says you." Marceline teased, doing her best to help the poor girl, but failing miserably and eventually breaking down into another laughing fit.
"Who knew after all these years you'd still need me to be your Knight when things start blowing up."
Bonnibel flushed as Marceline continued on her mini-rant.
"Jumping into my arms like a damsel in distress. You're kind of cute when you're scared Peebles."
"….Be quiet."

And then they fell deeply in love…..

Marceline woke to the sound of someone else rushing around her room. She opened her eyes blearily to see the nude form of her girlfriend getting up off the floor from where she had been rummaging, a bra and pants in her hand. "I'm sorry I woke you." Bonnibel said quickly, giving her lover a hurried kiss on the forehead, "It's just that I have to get to my kingdom before Peppermint Butler realizes I'm missing, and I can't find my shirt or underwear."
Marceline stretched and exited the bed, equally as naked as her girlfriend. The vampire walked towards her dresser and dug through it, eventually surfacing with a large band t-shirt.
"Here, wouldn't want my girl getting in trouble for indecent exposure. What kind of Knight would I be then?"

All was well…..

"I love you." Marceline murmured against Bonibel's bare thigh,which was beginning to gray under her teeth .
"I love you too."

Until it wasn't.

"I can't believe you're doing this to me!" Marceline screeched.
"I'm sorry,Marceline."
"It's Peppermint Butler's fault, isn't it!? Ever since he caught us-!"
"Enough, Marceline!" Bubblegum snapped then,after a shocked moment of silence,continued, "I love you, but my people have to come first."
"What does that have to do with anything?" Marceline whispered.
"I have to think about what's best for them. I can't have anything clouding my judgment, or-"
"Or what?" The vampire hissed.
"Or coming before them in my heart. I love you too much,Marceline. I'm sorry."
"Bonnibel-"
"You should probably leave."

Marceline traveled for many years, lived in many place, and met many people, but she never forgot Bonnibel, and eventually the two would meet again.

"You…kept the shirt I gave you?"
"I wear it all the time…as pajamas!"

And with past events put behind them for good

"Marceline…I'm sorry. For that time." Bonnibel whispered,and Marceline smiled a bit sadly.
"I know."

They fell in love for a second time.

"Marceline! Put me down!" Bonnibel shouted, clinging to her laughing girlfriend.
"What a Knights not allowed to rescue her princess from the castle?" Marceline said with a smirk as they flew over Ooo.
"Not when the castle is the home of that Princess." Bonnibel huffed, although Marceline knew that she was secretly amused.
"You needed a night off, anyway."

And lived Happily Ever After.