You should be able to have a meaningful, confidential relationship with your therapist.

However, therapy is meant to be a temporary part of our lives. Do you want your wife to become the person you lean on for support or find other relationships to help you manage in life? Your primary relationship with your therapist should be helping to develop these....not to be reinforcing you to hide from your wife or have your therapeutic relationship be the solitary reliable relationship in your life.

No, she shouldn't have read them, but if you think about it, it's pretty damn intimidating to have a significant other be so caught up in a relationship that is not with that significant other.