It was established yesterday that, lying or not being assertive is a behavioral problem or misconduct that is exhibited by those whose self-esteem is not healthy or whose perception of themselves is negative or poor.
It is expedient that you help your spouse to be assertive while you lead by example; do not say he or she can only lie to others or insult others but not you, for you will both bear the consequences of such insecurity.
Create a time to engage your spouse in a productive discussion on how to help one another improve their perception or estimation of themselves.