What is your current position at this job, and what is that woman position at this job. Maybe he just favors her because of her work ethics/skills and personality wise. Plus how does this affect your or others roles in your job. What is the age group range of these two individuals they sound pretty young and young people do socialize a lot. You mention he's married with children and you mention she is single. But how do you know that for sure. She could have somebody or could be married with children too and is your workplace a slow or busy atmosphere. Have anybody else notice what you have notice there. How do you know for sure this is going on. Most of the time when two people talk doesn't mean they have something going? To be honest if a person going to whistleblow they need what they're talking about and what the reason would be behind it? Is there really something going on where it needs to be address or is it out of a revenge thing? I would leave it alone because I wouldn't want to loose my job. But I'm curious to find out what happens. So keep us posted.