Is a divorce that I do not remember, but my wife confirms happened, considered a divorce?

If the wife claims that her husband divorced her, and the husband denies it, then the husband's word is to be accepted, unless the wife provides evidence of the divorce having occurred, because the original state is the continuation of the marriage. If there is no evidence, the correct approach is to administer an oath to the husband.

If the husband divorced his wife with three pronouncements, and the wife is certain of this, either through evidence or direct hearing, but the husband denies it, then it is not permissible for the wife to allow him to have conjugal relations with her. She must refrain from him, and ransom herself if she can, and flee from him. It is not permissible for her to remain with him.

If you do not recall divorcing her with that pronouncement, then it will not be legally counted against you. However, if the wife is certain that this divorce occurred, then she considers it as having taken place. So, if you divorce her with another pronouncement, this will be the second pronouncement for you legally, and the third for her in her belief. Therefore, she must ransom herself from you, and it is forbidden for her to remain with you.