How to forgive and forget?

Im so broken its been three years and the damage this person has done to me is crazy im letting all that shit get to me. I feel like im a bad mother (my babies dad hurt me so much) for some reason i cant forgive and forget i try and try but i cant every single day that shit is in my head how can u hurt someone that is carrying ur child and caring for them thats fucking crazy i don’t understand why this happens to me i dont even have the heart to ever hurt someone in any way. Like what did i do to deserve this im only 19 with a 15 month old and im broken im not the same i miss who i was. I used to be so happy and energetic but all this overthinking just gets to me... i dont know how to deal with this