Infidelity is not exactly a topic you wish to become an expert on. But when you suspect your girlfriend is cheating with a coworker, you feel compelled to gather information to either confirm or quash your fears.

You know what psychologists say about unfaithful women: They either change or become more focused on their appearance; they spend more time alone; they are frequently busy (or at least say they are); and they withdraw from physical contact. The fifth sign hurts most of all: Unfaithful women often spend more time at work, which brings you full circle.

For people inclined to stray, the workplace can be particularly alluring. It's already a place that brings like-minded people together in pursuit of a common goal. And it's where most people spend at least one-third of their waking hours. So it computes (at least mathematically) that about 36 percent of men and women admit to having had an affair with a coworker.

Statistics aren't doing your nerves any good. And you are further disadvantaged by not working for the same employer as your girlfriend. If you did, you'd be able to assess other signs of an office affair for yourself, such as whether your girlfriend and her paramour:

• Avoid eye contact, behave awkwardly or converse in a forced manner that suggests they are aware people are attentively watching and listening for clues. Leap to each other's defense in front of others. Often fail to get much work done.* Regularly show up together at places throughout the day.

You will have to assess the signs from a distance. Your accuracy will largely depend on how well you can establish your girlfriend's “baseline behavior,” or her habits related to her job. In other words, it will help you know her routine, so that any deviations (springing from the suspected liaison) will stand out. Be sure you know:

• When she usually leaves for work in the morning and what time she arrives. Whether she usually goes out for lunch, stays in the building or eats at her desk. When she usually leaves work for the day and arrives at home. Whether she is required to travel for her job and, if so, how often and the destinations. The prominent people in her “work circle.”

Knowing your girlfriend's normal behavior and routine should make it easier to spot changes that a workplace affair often trigger. They often include:

• Longer hours at the office. Paramours crave time together, even if it's in the workplace. But be careful that you're reading this clue accurately. If your girlfriend was recently promoted or has assumed responsibility for a time-sensitive project, longer hours might be justified – and totally innocent.

• Increase in work-related obligations. Part of the reason that workplace affairs are so common is that they're relatively easy to cover up. “I was working”; “I had to attend a seminar”; and “My boss wants me to start traveling” –

  all sound plausible. Dig a little deeper and try to learn why these obligations have suddenly increased – and in whose company they might put your girlfriend. More after-hours work calls, emails or texts. Paramours crave two-way communication, too. Without violating your girlfriend's privacy, try to get to the bottom of why and with whom there has been a surge in work-related communication. A sudden preference to attend work functions alone. That telltale sign about romantically involved coworkers avoiding eye contact may be able to fool coworkers, but it may not fool someone (like you) in her “personal circle.”

At some point when you're calm and rational, you will have to present your fears to your girlfriend. She may accuse you of over-reacting or trying to sabotage her career, which is common among unfaithful people; they often try to change the subject. Be persistent until she recognizes the futility in her denials. And realize that if you decide to forgive your girlfriend, many couples salvage their relationship after infidelity, especially if they rededicate to each other, undergo couples therapy and, in the process, become quasi-experts on infidelity after all.