The answer to your question depends on two other questions: Was your first marriage legal at the time? and If so, does your State recognise the first marriage as legal?
The answer to the second question is almost certainly Yes: this overview points out that "A marriage in another country is normally valid in the US; so, if someone is married in another country, they cannot get married again in the US or vice versa."
The answer to the first question depends on the laws of that country at that time, so you would need to consult a specialist. If, however, you are relying solely on the fact that neither of you registered the marriage, you may well be out of luck, since the USA is unusual in placing the onus on the married couple. Many Christian countries have a State church, and any marriage conducted by the rules of that church is legally binding; a marriage certificate is proof that the marriage took place, but is not required. If there is a question about whether the marriage was valid, the records will be consulted; and they are very carefully kept.
(As an example, in England a 'church wedding' in an Anglican church includes the formality of signing the register, which legally creates the marriage. The chuch sends off a six-monthly list to the relevant department. A 'marriage certificate' is optional, in case someone needs to check before the update, and do not wish to consult the parish register. Other weddings, from Catholic to atheist, must meet certain standards including having an official from the register office present; any 'church' that does not do so would be fraudulent if it charged a fee, so this is unlikely to happen. The official will register the wedding on the next working day, regardless of the actions of the parties.)
Of course, your wife cannot "sue you for bigamy"; the most she can do is report you to the police. The overview I quoted also says "A person who knowingly commits bigamy is guilty of a crime, but it is seldom prosecuted unless it is part of a fraudulent scheme to get another's property or some other felony." You would not, however, be able to marry again while the first marriage remains.