It wasn't even necessarily a mistake!
There is a risk attached to oral without, but the stuff you can catch tends to be easily curable - it was one of the bacterial ones, like chlamydia or gonorrhoea, wasn't it? If you like giving OWO and dislike giving OW, that can be a risk worth taking, for example, and there are lots of other reasons for people's choices. Sometimes it's fine, sometimes you catch something, but that doesn't make taking it a mistake.
You also have been testing, and that wasn't a mistake either.