If it turns out to be a case of infidelity, the husband needs to decide what he wants for his future. He could choose to forgive his wife if she is truly remorseful and committed to working on the relationship. They would then need to set boundaries and work on rebuilding trust. This might involve things like the wife being more transparent about her whereabouts and the people she meets.
They might consider seeking professional help, such as marriage counseling. A counselor can provide an objective view. The counselor could help the husband express his insecurities and the wife to explain her actions. In some cases, the couple may realize that their relationship has some underlying issues that need to be addressed, like lack of trust or communication problems.
One way is through open communication. The husband should calmly talk to his wife about what he saw and how it made him feel. For example, he could say, 'I saw you with that man and it really bothered me. I need to know what's going on.' The wife should be honest in return. Maybe it was just a misunderstanding, like she was with a co - worker on a work - related matter.