Herpes Doctor

My wife just got herpes from me. I have been faithful to my wife for the past eight years. She recently got the virus about a year ago. We have had sex before we got married and we also have had four children before her firts outbreak. I know that my wife and I feel that she has not cheated. I am having a hard time conviecing her that I have not cheated.
I am now 38 I did tell her (after we got diagnosed) that I may have contracted something when I was 17, but I was not sure. I did go to the doctor after noticing irritation and sores on my Penis, but he did not say it was herpes. He said it was a rash of some sort and prescribed medication. I have not had and outbreak that I can remember since, but after the actual confirmation I started researching pictures on the internet and it does appear that I had similar lessions.. I just want to know how can this lay dormant for this many years and after the children. We have had sex since we been married on a constant basis?????? Why now??????