...before? You're not in a the business of helping cheaters cheat, I know, but I figured it was worth a shot to ask anyway. There is no one I feel safe talking to about this.

Her Extramarital Relation Plans Endure Scrutiny

I'm not in the business of helping cheaters cheat*? You must be a new reader. Moving right along...

You could get an STI even while using condoms, HERPES. Condoms, used consistently and correctly, offer excellent protection against syphilis, gonorrhea, chlamydia, and HIV, but only some protection against herpes and HPV, which can be spread through skin-to-skin contact. (That's why so many wrestlers have herpes—not in their genital areas, but on the head, neck, and shoulders.) You can't get herpes or HPV sitting on toilets seats or though casual, incidental contact (shaking hands, waxing bikinis, etc.), HERPES, but you could get one or the other or both during protected sex with Loverboy—but only if he has one or the other or both. And unless you take up wrestling and your outbreak is shoulders-up, you won't be able to say you got it non-sexually.

All that said...

CDC:

Most people who have genital herpes have no symptoms, or have very mild symptoms. You may not notice mild symptoms or you may mistake them for another skin condition, such as a pimple or ingrown hair. Because of this, most people who have herpes do not know it.... A herpes blood test can help determine if you have herpes infection. It cannot tell you who gave you the infection or how long you have been infected.

Planned Parenthood:

Herpes is easily spread from skin-to-skin contact with someone who has the virus. You can get it when your genitals and/or mouth touch their genitals and/or mouth—usually during oral, anal, and vaginal sex.... Herpes is most contagious when sores are open and wet, because fluid from herpes blisters easily spreads the virus. But herpes can also “shed” and get passed to others when there are no sores and your skin looks totally normal. Most people get herpes from someone who doesn’t have any sores. It may live in your body for years without causing any symptoms, so it’s really hard to know for sure when and how you got it. That’s why so many people have herpes—it’s a pretty sneaky infection.

You could already have herpes, your husband could already have herpes, Loverboy could already have herpes, and odds are good all three of you already have HPV**. If you have an outbreak after hooking up with Loverboy, you could argue—with a straight-ish face and a clear-ish conscience—that you must've gotten it before you were married and you're only having your first outbreak now. And it might even be the truth.

* I'm actually not in the business of helping cheaters cheat. But there are circumstances where I believe cheating is the least worst option for all involved, sometimes a person's gotta do what she's gotta do to stay married and stay sane, "the victim of the affair is not always the victim of the marriage," as the great Esther Perel says, and for all I know cheating may be the least worst option for you, your kids, and your husband. Regardless, HERPES, you didn't ask me to weigh in on the reasons why you're cheating, only the potential for being outed as a cheater by a herpes outbreak, and didn't offer the kind of details I would need about your marriage to make a definitive ruling. So I stuck to answering the question you asked.

** Everybody please get your kids vaccinated—get your adult self vaccinated too.