I'll say it again.
No emotional reaction is EVER wrong.
You feel what you feel.
Never use strangling language on yourself or others such as:
"You should feel X" or "You shouldn't feel X"
You should feel what you feel because you do.
It's that simple.
The thing to do is to give yourself and anyone else who feels a certain way, an oportunity to explore the whys of the feeling.
The "whys" are NEVER wrong either, because these too are "feelings".
Use active listening with yourself or others to explore the feelings whether these are bitterness or other powerful emotions which feel unpleasant.
(I won't use the term "negative" as applied to emotion because even that language choice condemns the one having the feeling)
Brainstorm, the canvas, the landscape and the world of the feeling to see where it's strongest and give it the understanding. Spend A LOT of time with it, exploring the terrain. Get a sense of the textures, the sounds, the sights of the feeling and know it. Be the emotion completely.
The emotion will feel understood, accepted, justified and then the emotion will dissipate and you will understand yourself and the factors which lead you to the world where that emotion lives.
Don't try to destroy the world of the emotion because it is a part of you as well, and it has its place.
Let it breathe and it will stop shoving you under the water to survive.