If you do any research into the topic of infidelity you will find that it is extremely rare that condoms are ever used and it is for that reason that it is strongly recommended that testing for STIs are done when an affair is discovered. Because most of the time symptoms aren't apparent, in many cases 70% of the time and even less so in women, STIs can be passed between affair partners and then to their respective spouses and even back again. Often, if two people in an affair discover an STI they get treatment and never inform their spouses who may also be infected - there is no requirement under the law to inform the spouse of a person with an STI unless it is HIV/AIDS. Even things as dangerous as syphillis do not have mandatory spousal reporting requirements anymore. And HIPAA laws won't even allow a spouse to find out if their cheating spouse had ever been treated for an STI.
Since there is a real difference between what married women do when they are in affairs with respect to their spouse - far more often than not they cut back the frequency or the time between sex with their partners or cut it off entirely the risk of spreading STI in that direction is not as high. On the other hand when it comes to married men involved in an affair they almost always have no change in their sex life with their spouse at all - no matter what they say to their affair partner it is almost surely a lie - and thus the risk of STI spread is greater in that direction and the risk of re-infection especially if the married man's spouse shows no symptoms.
Many times no birth control is used at all, not even the pill. It is estimated that 10% of the married men out there at any given time are raising a kid that isn't biologically theirs and they don't know that at all. So, it is never wise to think that people involved in affairs think or even care about such consequences when they are carrying on their escapades. It is a fantasy world of rainbows and unicorns where even when the unicorns fart it smells like bubble gum and cotton candy.
It is rather chilling to know that people will endanger their partners lives like that but they do almost all of the time without giving it a second thought. So beware of projecting any thoughts that people involved in affairs are thinking about anything, let alone about how it could affect, their health, their spouse's health, etc. Considering that even in the best case, if the affair partners leave spouses and think they are really in love and will live happily ever after together, 95% end in disaster.
All of the risk, all of the damage, not just to their kids, not just to their spouse, but even to themselves is undertaken for - well, nothing but misery, pain, and the destruction of two households not to mention the effects to other relationships with family, in-laws, friends, co-workers, etc.
It is beyond me why people would affirmatively choose such paths (it is not an accident, or a mistake) when so many other options are available yet that is what they do.
