I have the virus. Only instead of getting a sore on my mouth, I get one in my genital area. This is not a confession or a lecture, simply the sharing of information between two people. Avoid loaded words like 'awful', 'disgusting', or 'incurable'. Luckily it's both treatable and manageable.
Many people practice by telling a friend first.
It builds up your confidence and gives you a feel for the kind of questions others might ask. Plus, the more people you tell, the easier it gets. Another good idea is to role-play the situation with a friend who's already in the know. But don't let them always play the understanding partner. It's important to prepare for a variety of situations - not just the easy ones.