herpes can hide in your body and never give you an outbreak.
a lot of people spread it without knowing they have it. its a bizarre virus and very interesting.

now if she came home with "the clap" that would be evidence of an affair but herpes is not.

has her health been stressed lately? has she been stressed lately?
you say you have been married 25 years so i wonder if its pre-menopausal hormone flux that is giving her an outbreak....?

why didnt she tell you she had it before you were married?

Genital Herpes can be HSV1 or HSV2. If HSV1, common name cold sore, she can self-infected herself by touching her mouth, then touch herself below. Whether this outbreak is first episode or not, we don't know. She might have some outbreaks before and not aware of;only recently she noticed the symptom. You can hire a detective to tape or camera your wife if you suspect she had been not faithful. My co-worker hired a detective to catch his wife's infidelity, and this gave me the idea. However, if you are not going to do anything about that, it might be wise not to waste money.