Why would my wife tell me this about her coworker?

My wife and I met in college and have been married for 9 years. We are both in our early thirties. We have only been with each other and have always had a good life I think. However, recently we have been arguing. This has especially been the case since she told me about a coworker (she is a school teacher) who has been paying her many compliments and what I feel is too much attention. For example, she says he described his physical "ideal woman" to her one morning and it was someone exactly like her. He has apparently suggested on two occasions she leave one more on undone on her shirts. He also rested his hand on her backside after a hug and another time told her he could see what she was wearing through her skirt. He is a single guy in his twenties I think and I do not like this going on. My main question though is why she would tell me this stuff when it makes me so upset? What do I do to handle this? I do not want a confrontation but I also do not want this going on. What do I say to her or to him to make sure that this does not get out of hand?