I wasn't cheated on, but my father was and he is still with her.
My parents were high school sweethearts who got married 2 years after graduation. My mother had an affair starting ~6 years into their marriage right after my sister was born. I was 2 and my brother was 4. I was never directly aware of what was going on, but my father filled me in when I turned 18 and it brought up all kinds of memories that I always figured were just misunderstandings on my part.
My mother was emotionally and somewhat physically abusive towards us all during this time, with my father obviously getting the worst of it. She would tell him she was going to leave with us kids to be with her "lover" or to live with some of her friends. If my father were to divorce her she said she would tell the courts he was abusive towards the whole family so that he couldn't see us and take him for all his money. He said he didn't have the heart to end his life on his own because of us kids and since his life insurance wouldn't go towards us if it was suicide. He broke down at work regularly and he was the talk of the office apparently.
My parents went to marriage counseling, where the counselor only urged for immediate divorce, saying it was not at all worth the pain. My dad was too terrified of losing us and he felt they were just legitimizing my mother's behavior. They prescribed antidepressants for my dad to deal with it but he refused to take them since he said they made him feel content with a situation that was horrible for him.
After my mother's "lover" broke up with her they would still meet sometimes. Then at some point he got married to another girlfriend of his and my mother apparently started going to counseling to deal with the breakup. She was put on antidepressants and this is when my dad said her behavior towards him improved and she started loving him again. He says he feels her love is disingenuous because of the drugs but he still accepts it and loves her.
He told me recently that up until age 40 he dreaded the future and wanted his life to end. He says now, in his late 40s, he finally embraces the future loves living. He's happy now, but it tainted the experience of watching his three children grow up within a broken home and watching it all through a depressed and heartbroken mind.
It's not worth wasting your life with someone who cheats. I'm glad my dad stuck with us instead of just willynilly getting a divorce like the marriage counselor urged him to do because he WOULD have lost everything and I would have ended up growing up in a trailer park with a 100% abusive environment instead of a decent upper-middle-class home. But he could have raised us in a more healthy environment for himself and his kids if he had gathered the readily available evidence he needed to not lose out in a divorce.