5. We notice and understand body language
Women are known to have a sixth sense, especially if it concerns relationships. We always notice and analyze all small details in another person, and that includes body language of our partners. So we usually are aware of his sympathy to a colleague, which we have never met.
Once we notice something suspicious, it starts bothering us, though we may not be even aware of what exactly annoys us. And if a woman suspects something, she will be very upset when her man doesn`t spend time with her but stays in the office.