If you're the one feeling bitter because someone hurt you, the best thing to do is to forgive that person even though you don't feel like it. Hanging on to bitterness will only cause you to hurt yourself more and it will erect a wall between you and your loved ones. God has called us to have peace with everyone. If someone hurts you, go to that person and tell him/her how you are feeling and, no matter the reaction, choose to forgive.
Benjamin Franklin said:
"We stand at the crossroads, each minute, each hour, each day, making choices. We choose the thoughts we allow ourselves to think, the passions we allow ourselves to feel, and the actions we allow ourselves to perform. Each choice is made in the context of whatever value system we’ve selected to govern our lives. In selecting that value system, we are, in a very real way, making the most important choice we will ever make".
So, even though you don't feel like forgiving (as we all do), pray about it and decide it in your heart.
On the other hand, if someone is bitter or is holding something against you, talk to that person and ask for their forgiveness. Then, try extra hard to serve them and love them.
I hope this helped
