How do you forget and forgive a person who betrayed and used you?

This can be very difficult. Even at the time of the Prophet Muhammad ﷺ when his uncle was killed by Wahshi, he said to Wahshi, when I see you it reminds me of my uncle. So it was difficult even for the Prophet ﷺ when he experienced these difficult times. It is a normal human emotion, a normal human feeling that we should not try and brush under the carpet. But what we do have in terms of advice from the Prophet ﷺ as to how we can deal with this is he ﷺ said that forgive others and Allah will forgive you. Irhamu turhamu, have mercy on others and Allah will have mercy on you. The hadith is by Muslim. So although it will take time, although it is difficult, if you keep reminding yourself that the bigger goal, the bigger aim is with Allah, is with the Akhirah, this life is temporary, keep having that focus and prioritizing that. Inshallah, over time that will diminish in terms of the feelings that you have.