You also can get other infections by having oral sex. Unless there are cuts in the mouth that the virus can get into, it is unlikely that a person with HIV will give it to the other person by having oral sex. When people share love and sex, they really trust each other, and they have special ways of touching and talking that they don't do with other people. It is a different kind of touching than parents do with their children, and it is very private. And if someone breaks a promise like that it can hurt their wife's or husband's feelings very deeply, and make it hard for the couple to keep loving and trusting each other.
Some couples end up getting divorced.
But sometimes, when someone has sex with someone who isn't their wife or husband, they feel really bad afterwards, and they ask their wife or husband to forgive them. And many couples stay together and love each other very much even after the promise is broken and one person has sex with someone else. I don't know what private promises the President and his wife made to each other. But the President has come forward and said he did something wrong. We do think it's wrong to break a promise, especially a really important promise made to a wife or husband, boyfriend or girlfriend.