Hebrews 12:14-15 Pursue peace with all people, and holiness, without which no one will see the Lord: looking carefully lest anyone fall short of the grace of God; lest any root of bitterness springing up cause trouble, and by this many become defiled;
Follow peace and holiness and steer clear of bitterness. Scripture says
in Romans "If it be possible, as much as lies in you, live peaceably with all men." Peace is sometimes difficult to have, however as much as it is possible do so. Be at peace with yourself to guard yourself from bitterness.
It is difficult for bitter people to have healthy relationships. They see everything through a critical lens. When we learn to appreciate what we have and those around us, bitterness drifts away and is replaced with gratefulness.
If the whole world seems to be so ugly for you, maybe you should take a look at the windows you are looking through. Are you looking through windows of faith, believing that God will do exceedingly abundantly above and beyond in your life or are you seeing life so bad and unfair because you didn't get your way?
Trust God and ask for His perfect will in your life. I like this quote by Spurgeon. "A bitter spirit is a poor companion for a renewed heart." -C Spurgeon
To steer clear of bitterness, have the attitude that no one owes you anything. Life isn't always fair, but God is fair. It says in 2 Thessalonians 1:6 that "God is just..." There is no reason to get bent out of shape and bitter. God will set all your crooked places straight when you stay in faith and pursue holiness.
Write down in your journal* the areas in your life where you feel bitter. Ask Jesus to remove that bitter root so you will not produce bitter fruit in your life.
Have a blessed day in The Lord,
*I strongly recommend getting a journal if you don't already have one. Write down the dreams God has placed in your heart and back them up with scripture, believe for God's perfect will in your life. :-)