Can A Married Man & A Single Woman Be Just Friends?

I have a friend who has been married for almost 4 years. Her husband works at a hotel where he is friends with a girl who he says is just his friend. The problem is that after working together 5 or 6 days together per week they still have to be constantly on the phone and spending their off days together. Sometimes she will go to his yard in the evenings and they will be outside in her vehicle 'chatting' for hours on end. I know if it was my husband I would have gone out to that car and cause some ruckus in the neighborhood.

The wife is saying that although she is uncomfortable with their 'friendship' she does not want to cause any waves because she wants her marriage...... Honey I would have been causing a Tsunami instead of waves because I would not be keeping my mouth shut so that he thinks that i'm some docile person that he can walk all over. Hell no! He must think twice before he starts that bull with me.