Is reporting child abuse to the wife of the abuser a good idea?

Many years ago, when I was a teenager, an adult friend touched me inappropriately several times. I finally found the courage and told him to stop and he did. We sort of pretended that it had never occurred. Nevertheless, he now has children on his own and I am worried. I want to inform his wife about those actions that occurred in the past. I don't want to involve authorities. I would consider him still a friend. But what he did may have been just the beginning of a career as a pedophile. Someone needs to know. If I write a letter to the wife, is this libel? Are there better ways?