Two possibilities exist: you are cheating on your wife or you are not. The truth is something that your wife must accept. When someone denies reality and believes in something, when objective evidence proves it not to be true, then this is very close to the definition of a delusion. Your wife may be delusional.
If considering that possibility, her delusions might have been exacerbated by her giving birth. Postpartum psychosis is a rare condition in which a woman develops psychotic symptoms following childbirth. Some of the symptoms can include: delusions and unusual beliefs, suspiciousness and paranoia, hallucinations, mood swings, irritability, and the decreased need for sleep. Based upon your letter, your wife has several of those symptoms.
Given that her fears are unrelenting, professional intervention is needed. A mental health professional can evaluate her symptoms and determine what might be wrong. Once a diagnosis is made, her symptoms can be treated with professional help. Medication might help to decrease or eliminate her symptoms.
If your wife is unwilling to seek treatment , then you should consult a mental health professional or attempt marriage counseling with her in attendance. A therapist can assist you in determining how to properly handle this situation. Please take care.
Dr. Kristina Randle