Why is it so hard to forgive,and not take revenge on them?

In the bible it says you should forgive.. but forgiving isnt always easy is it?
    Why is it soo hard to forgive someone and don't take revenge on them when ever they arnt looking?
 When someone brakes my heart this question pops up alot! I Mean when you get cheated on 5 times in the exact same week with your best friend.. you want to do  something  ... you want to hit him in the face or you wanna make his life not easy to live with and make him go threw the same pain you felt. Its hard to forgive someone that does hurtful things to you.that you prolly wont forget huh? Sometimes.. you say you forgive them but do you really? Most of the time you would answer this question with a "kinda or yes" .but maybe if you do ...are you gonna forget it? prolly not! Its going to become a memory that you'll have ..and every time you see that person that hurt you.. you might feel anger..or sadness  because you think.. "what did i do to deserve this or why did this happen to me?" and really.. theres nothing wrong with you...
 But the question is Why is it so hard to forgive?  Its Just hard to forgive when you have  it set in your mind that the person you thought would never hurt you did.. and maybe its just hard to forgive when your afraid of forgiveness your self and thinking they may do it again
  Thanks for reading hayley

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