i had some rough patches back in middle school with a friend. due to some toxic stuff going on in the friendship, i wasn't always treated fairly, and lot of bitterness came from that. i carried this resentment with me into high school, and as a result of refusing to let go, the bitterness turned me into a bitter person. i didn't exactly treat my friend well, and instead of talking it out or admitting i was wrong for acting that way, i came up with every excuse i could for why it was okay. i realized after a couple of months that not only was i hurting her, but i was hurting myself. there was no way for me to heal if i kept holding onto that bitterness. look, getting hurt sucks, especially if it's by someone you love. but the only way to move on is to let go and forgive. i'm not saying it's okay for them to mistreat you, but whether the other person is sorry or not, you owe it to yourself to find peace. hurting them is not going to fix anything; it's only going to cause you more pain. but letting go of that anger is how you grow. you can't take hold of happiness if you're holding onto a grudge.
forgiveness is a choice. i didn't understand that a first; i thought i couldn't help being angry, that i would just have to keep feeling that way until one day i woke up completely over it. sadly, it doesn't work that way. it'd probably be easier if it did. instead, you have to choose to not be angry any more. you have to begin to look at them though god's eyes and understand that god still loves them just as much as he loves you, and they deserve forgiveness just as much as you do. when you train your mind to stop thinking hateful thoughts towards them, you're able to stop feeling that bitterness. i encourage you to forgive endlessly. life is too short to spend your time being angry.