1. You don't have to forgive. Our spiritual leaders (and Facebook feeds) encourage the idea that forgiveness helps us heal — there's that saying, "Holding onto anger is like drinking poison and expecting the other person to die," which is a fine saying, but it glosses over the fact that anger can be useful; anger can serve as a way of asserting your value, make it clear that someone's behavior is unacceptable. Girls, especially, need reassurance that they don't always have to make nice. (Girls, you don't always have to make nice.) Anger can also be a way to take a stand on the larger concerns surrounding your individual experience (e.g., racism, misogyny and other social justice issues).
2. Assess. What was the level of betrayal? Was the act criminal or simply the jerkish behavior humans are prone to from time to time? Is this a person trying to find his or her way in life and making mistakes that caused your pain or is he or she a trusted figure who took advantage of you? Have you wronged people, intentionally or not, in the same manner? Or is the offense so far beyond anything you would ever do to another human being that you can't relate at all? On your personal scale, was the act in question an infraction, misdemeanor or felony? Are you prepared to be judged as harshly as you're judging others? How often do you have to interact with the person who hurt you? When you see this person — as you inevitably will if he or she lives in this same small town and shares social media — do you feel annoyance or fear? Do you simply shake your head and cross the street or does your stomach clench so hard you think you might have to lean over and vomit into the gutter? (Or, as a friend of mine suggested, "Do you want to just stab this person in the face over and over until bone fragments are flying through the air like confetti and all signs of life have vanished from his [or her] goddamn eyeballs?")
3. Use the above calculations to determine your leanings toward forgiveness. Maybe the affront wasn't malicious, you've realized. Maybe the benefits of moving on unburdened by hate are worth the letting go. Maybe you really are ready to forgive. You are? Congratulations! Unsurprisingly, the Internet is full of how-tos on this one, everything from "Remember we are all one," to "Be prepared to clearly articulate what the person did that offended you." Find the advice that resonates with your divine and/or practical self and follow it. Do note that if you're going to say to someone, through words or actions, "I forgive you," you have to really do it. Flinging a grudge back at someone after you've given him or her reason to think things are cool is not cool.
4. You don't get to be bitter. If forgiving is beyond you, that's fine, but if your pain eats away at you daily, if it keeps you awake at night, distracts you from the moments in your life that should be joyful and productive, if all your conversations with your friends turn again and again to the same topic, then you need to do some work. Healthy anger is one thing. Obsessive loathing is another. Write uncensored, unedited rants, then turn the computer off in favor of juicy books, gripping podcasts, silly movies and excursions with your most supportive friends during which you ask them all about their lives. Memorize the multiplication and/or periodic tables so you can recite them in your head whenever you find yourself thinking about how you were wronged. If you still find the ratio of hatred to happiness skews ugly, get counseling. You will be happier refusing to wallow in hatred, for not allowing the hurt inflicted upon you to define your life.
5. Understand that the real benefit here is making peace, not necessarily with the person, but within yourself. If a wrong can be made right by hashing out the what and why of it, by mutually agreeing on the mistakes that were made, how to resolve them and how to move forward, that is a grand and wonderful thing. In a just world, most of our conflicts would be solvable. However, if the best you can do is try to avoid the people and situations that trigger the post-trauma shakes, that's OK — it's not your fault. Keep working on it. Because you are so much more than a victim. Life offers so much more than this one shitty act. The beach. The forest. Skinny-dipping. Goat cheese-stuffed dates drizzled with hot pepper oil. Frisbee. Exile the perpetrator from your existence to the greatest degree possible, then turn around and embrace the people who've stood by you with enough love to outshine everything else.
BONUS: This won't work in all cases — I'm sorry for that — but if you can, find humor, dark as it may be, in your story. Seek out comedians and writers who've wrung funny from horrible. Revel in them. When you're able to relay to people what happened with a shrug instead of tears, that's a sign of healing. When you're able to convey that a horrible, messed-up thing happened to you, but finish with a laugh, you've won.