What options do I have if my wife had an extramarital affair and became pregnant from the said affair?

You can file for divorce and allege disestablishment of paternity. Because you are married you will be the child's legal father if you do nothing. If you file now you can put the court on notice that her pregnancy bills should not be your responsibility. If you and your wife decide to stay married and raise the child (it happens) you do my have to do anything unless the actual biological father brings a paternity suit. For more information and actual legal advice on the facts of your situation you should consult with a local, experienced and reputable family law attorney.