It's no surprise to anyone that sometimes people suck. Occasionally we start relationships or friendships with people who turn out to be different than we originally thought they were, and those people hurt us.
We can't control what other people do to offend us or make us angry, but what we choose to do with this anger sets us apart. You can either let it define your relationship with that person, and hold whatever they did against them forever, or you can decide not to let that negativity affect you, and move on. In my opinion, the latter is the better option.
Holding grudges and anger in your heart for someone only holds YOU down, and holding a grudge brings unnecessary negativity into your life. Let's face it, it also kind of makes you look like a jerk. I'm just as guilty as anyone else when it comes to letting my negative feelings towards someone affect how I might look at them in future situations.
However, I have found that when I take a minute to think about it, everyone makes mistakes, so why should I be dwelling on one person's forever? People change and grow, and sometimes what they did in the past no longer defines who they are in the present. I wouldn't want someone I acted wrongly against three years ago to judge me now on the person I was then (seriously, she sucked).
All this being said, it is important to forgive people, to let go of whatever negativity you may hold in your heart for someone, and to let yourself be free of that burden. This is not saying that you need to welcome everyone who has ever hurt you back into your life with open arms, but you don't have to hold onto hate forever.
Coming from personal experience, it is so much easier to move on from a painful situation when you have peace of mind. Forgiveness allows you to acknowledge what you went through, to let go of any pent-up resentment, and to move on with your life. Letting anger linger for a certain person keeps them in your life, and continues to give them power over you. Once you are no longer being held down by negativity, it's amazing how much more you can flourish.
Strive to fill your life with nothing but positivity, and let what's past be past. Don't let forgiveness blind you though. Earlier this year, I let someone back into my life who although I had forgiven for the hurt they had caused me, should not have been back in my good graces. They took advantage of the fact that I had forgiven them to once again walk all over me.
You can forgive someone for what they've done, but sometimes people never change. I guess what I'm trying to say is, it's okay to forgive someone and let go of the resentment you hold towards them, and to never speak to them again after that. Forgiveness should be for you and your personal healing, not for anyone else.
Don't confuse forgiving what has been done with allowing people to hurt you time and time again. Let go of grudges, and don't let past anger run your life, but don't let them blind you from seeing people's true colors either. Forgiveness has the power to heal your heart, so take my advice: let it.