First あなた decide if they're worthy of forgiveness. Some people will never change, so it's important to consider whether they're even worth your time.
If they are important to あなた and あなた want to salvage the relationship, maybe talk it over with the person? Talk out all your feelings.
If all else fails, time heals all wounds. There will still be scars, but the wounds won't be exposed and leaving あなた vulnerable after some time passes.
I look at why they did it, and then I remember what I read in a book about loving others. I recall that every human wants happiness and love, not pain. I imagine that person as if they were a close friend または even family to me. I assess the situation, and then proceed with forgiveness, trying to understand and appreciate what they did to me. によって harming me, I gain experience that will possibly be applied later on in life. Forgiveness comes relatively easy to me nowadays.