Is he considered sinful, the one who divorced his wife due to the interference of her family, her behavior, her discovery of his infertility, and her disclosure of the secret?

You are not sinful for divorcing your wife; rather, you have acted righteously by divorcing her after she requested it. If a wife asks her husband for a khul' (divorce at her request) in exchange for a compensation, it is commendable for him to agree to her request. So, if you divorced her and fulfilled her rights, you have shown her kindness.