Bitter!

If you deal with the hurt, have a forgiving spirit, make reconciliation, then God's grace will take over and you will not become bitter. But a bitter person is one who refuses to deal with a problem, harbors hostility in his heart, and then must try to justify the feeling that he has. So he becomes a negative person, looking for other things that are wrong in order to justify the way that he feels. God will convict us for having wrong feelings toward others, but the bitter person is at controversy with God. He tells God that he has every right to feel the way he feels and begins to look around for other reasons to justify this. The more he sees, the more bitter he becomes.

What does Bible say about it?

James 3: 8-18
8but no man can tame the tongue. It is a restless evil, full of deadly poison.
9With the tongue we praise our Lord and Father, and with it we curse men, who have been made in God's likeness. 10Out of the same mouth come praise and cursing. My brothers, this should not be. 11Can both fresh water and salt[1] water flow from the same spring? 12My brothers, can a fig tree bear olives, or a grapevine bear figs? Neither can a salt spring produce fresh water. 13Who is wise and understanding among you? Let him show it by his good life, by deeds done in the humility that comes from wisdom. 14But if you harbor bitter envy and selfish ambition in your hearts, do not boast about it or deny the truth. 15Such "wisdom" does not come down from heaven but is earthly, unspiritual, of the devil. 16For where you have envy and selfish ambition, there you find disorder and every evil practice.
17But the wisdom that comes from heaven is first of all pure; then peace-loving, considerate, submissive, full of mercy and good fruit, impartial and sincere. 18Peacemakers who sow in peace raise a harvest of righteousness.

Mark 9 : 49-50
49Everyone will be salted with fire.
50"Salt is good, but if it loses its saltiness, how can you make it salty again? Have salt in yourselves, and be at peace with each other."