Relationship of Marcy and PB

Why is Marcy Jelous of PB? We watched I Remember you,and this ep explored The Mushroom War and The True Soul of Simon. We also found out who gave Hambo and the Enchiridion's Discovery. Do u guys remember when Marcy frowned when IK began to sing of Bubblegum. Marcy likes IK and she doesn't like him to like Bubblegum. My theroy is that they used to be friends like when Marcy even knew her first name (Bonnibel).

Marcy is Jelous because of Ice King.

Oh Bubblegum01:16

Oh Bubblegum

The proof: