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It may not be. There is no sure way to tell if he is being truthful. You are right, people with narcissistic personality disorders use manipulation as a way to get what they want and not telling the truth falls in that category. Many people with this problem become very good at not telling the truth and therefore, it is very difficult to determine if they are telling the truth when they claim they are.
You should go with how you feel about this situation and if you want to continue with the relationship. If you already suspect that he is not telling the truth and he is twisting the situation to his advantage, then the basic trust needed to continue your marriage and give it a good foundation is not there. You can try counseling, but since you will never be sure if he is telling the truth, then again it will be up to you to decide if the risk of staying married is worth the cost.
I hope this helped,Kate