Okay, here is my idea on Bubbline...

When watching "What was missing" I did not see any proof of Bubblegum and Marceline dating until people started to really dig into it. My idea is that they never dated, though there could be a possibility that they were in some type of relationship.

In "What Was Missing", I did notice the part where Marceline says to Bubblegum "Looks like you're not as perfect as you thought. I guess you cant judge me anymore."

What i thought for just a moment was that maybe they were really good friends and Bubblegum judged her for "Not being so perfect"? But then there was also a question. Not perfect at what?

Like, I’m very confused about where people got the idea that they are dating or were dating.