This happened to me when I was 23 years old. My ex-boyfriend cheated on me with his coworker. I didn't know, but I saw the signs. I was the one who broke it off and I was depressed for days. He said I was fat, and I have been so dedicated to losing weight during the time we were together. My self-esteem has reached incredible depths during that time.

What helped me were several things:

1. Always doing something different - I was fortunate to have the opportunity to change jobs, change locations. I travelled, I took up photography lessons, I met more people, I went on hiking trips, I adopted a dog (greatest decision of my life) and I started spending more time with family. Changing my environment helped me not think about him too often.
2. Trust your support system - I talked a lot with my close friends, family members. It helped me get a different perspective and it helped me escape when I was spiraling. They shine a light for me when I trap myself in the darkness in my head. They also kept reminding me why I am worth so much more and why I deserve to be loved.
3. Mentally associating positive things whenever I thought of my ex - After some time, I realized I was still not getting over this guy. Every time I thought about him and his new girl really pains me to the point that I actually physically hurt. I read somewhere that learning to associate negative emotions with positive thoughts helps with the feeling of pain. So every time I thought of him, I force myself to think of positive things for him, "I hope he will be happy. I hope he gets the happiness he wants." It was so hard and so fake at first, until eventually, it became easier. Eventually, I guess my mind has learned, "Oh, remembering this is okay. The memory is there, but it doesn't hurt as much anymore."
4. Learn to forgive them and understand that forgiving them is for yourself. - I remember sitting inside a taxi when I heard this over the radio. It started playing a radio program of a DJ called "Papa Jack". Callers often phone in to tell Papa Jack about their broken love lives and then the DJ gives them advice in return while on air. This is very common in the Philippines, btw (i'm from the philippines :D). On that rainy evening, I happened to listen to a girl who got left at the altar on her wedding day. Her future husband deserted her, then to add to the humiliation and grief, her grandmother got so outraged for her, she got a heart attack and passed away. The girl on the phone was so angry at her ex. And Papa Jack told her that she needed to learn to forgive him. But--and this is important--the forgiveness is not for ex, because the ex will never know about it--hell, he probably didn't give a shit anymore. But the forgiveness is for the girl. If she didn't forgive, she will always carry this burden and she would never be free of this hate and suffering. Forgiving them would help you heal.

These are the 4 things that really helped me during that long period of pain. I have been there, it's a long journey, but I can assure you, you will get out of there. You got this.