Welcome to Just Answer and thanks for your question. There is no cure for genital herpes. There are antiviral medications that can be used daily to help prevent outbreaks. One is less likely to pass along herpes when there is not an outbreak, but sometimes the virus will shed without having blisters, so it is still possible.
You are correct that it isn't always transmitted. Some people do go longer and longer times between outbreaks, even years. For those people their immune systems may be keeping it in check. Other herpes viruses can also remain quiet for years without causing a problem. Shingles (herpes varicella) is one of these. Other people can have a genital herpes outbreak every other month. There is no way to calculate the risk for any given person due to the individual makeup of a person's immune system. When there has not been an outbreak in years, many couples decide to forego any protection, especially since while herpes is uncomfortable, it isn't a life-threatening disease.