Whether to confront or not is totally your decision. With that said, if she finds out you knew and said nothing then she will lose any shred of respect for you she might have left. Back to the doormat thing. The only time not to confront is if you're going to blindside her with divorce papers and are gathering evidence before she knows you're looking.
To save the marriage, if you want to, then you have to refuse to be disrespected like this.
