We will focus on the what happen in the past that they both had to get rid of feelings for each other
After the fall Diavolo and Mammon hang out a lot because they both enjoyed raising kids and satan was a newly born kid
Through that excuse they both hang out for along time they knew each other better than anyone else and they both developed feelings for each other
Diavolo : Im going to confess today!
With mammon
Mammon : Im going to confess today!
They both decided to confess to each other one day
In their usual meeting spot which was the brightest place in devildom but it was still very dark since devildom doesnt have sun
Diavolo and Mammon met up and were going to tell their feelings
Diavolo : Mammon I wanted to tell you something
Mammon : What a coincidence same
Diavolo : You go 1st
Mammon : okay dia I-
Mammon was interrupted
Guard : Lord Diavolo!
Diavolo : Yes?
Guard : The brothers are traitors and nothing else the whole devildom thinks that and that scummy second born is just deceiving you!!!!!
Diavolo was enraged while mammon was shocked of such accusations and being called "scummy"
Diavolo : WHAT PROOF DO YOU HAVE TO BACK UP YOUR FOOLISH AND ARROGANT WORDS?!
Guard : S-sir their ex-angels they might be here for spying
Diavolo turned into his demon form and held the guard's throat
Diavolo : SUCH FOOLISH WORDS YOU DONT EVEN KNOW THEM!!
Guard : S----sorry....
The guard was having trouble breathing
Barbatos comes and frees the guard
Barbatos : My lord I understand what level of foolishness has this man done I will deal with him
Diavolo : Okay I will leave him to you
Barbatos bows and leaves with the guard
Mammon : Diavolo...
Diavolo was stunned since mammon usually called him "Dia"
Diavolo : Mammon im sorry that happen!
Mammon : if this me and my brothers image here I don't want to be here...
Diavolo : Mammon I will solve it out
Mammon : Maybe we shouldn't hang out...
Diavolo : Mammon please no!
Mammon : I will stay at devildom but I wont hangout with you anymore
Heartbroken mammon leaves a heartbroken diavolo
They both tried to move on but it led to the current story events
See you all in the next chapter