Marrried but obsesed with another man

I am 30 years old and have been married for 7 years and have two small children. Recently, we have been having an addition added on to our home. The problem is, I am extremely attracted to the builder who is working on our house. I think about him night and day. He is engaged to be married in October but they do not get along (hear them fighting on the phone several times a day). He will say things to me like he would have to be crazy to get married to her because they will be divorced in 6 months. He has not made any moves on me (why would he since I am married and my husband and I are paying him) but I long to tell him how I feel. I am just looking for something physical as I would not want to be in an actual relationship with this man. I do not want to hurt my husband who I know loves me very much. This feels like a mid-life crisis (is 30 too young for this?) but this man will be finished here in a few weeks and I am crushed at the thought of never seeing him again. How can I actually want to risk my family for this?? Please tell me what you think I should do.