In omitting information and telling half-truths you can claim you aren't "lying", but it is still a deception. I think I prefer the person who lies to me outright than the one who manipulates the truth in this way and then tries to self-righteously claim to be an honest person. Don't play games with the truth. Deceiving someone who trusts you is one of the most hurtful pains you can inflict, and it never fully heals.
Proverbs 6:16-19 New International Version (NIV) 16 There are six things the Lord hates, seven that are detestable to him: 17 haughty eyes, a lying tongue, hands that shed innocent blood, 18 a heart that devises wicked schemes, feet that are quick to rush into evil, 19 a false witness who pours out lies and a person who stirs up conflict in the community. ...Confess and repent if one of these sins are yours.
I'm the type of person who doesn't enjoy hanging out second chances. But if I do decide to forgive you for whatever you've done, don't ever think I'll forget. Thinks will never really be the same between us again.
Plus it is always done behind closed doors, no one ever sees the true colours of the narcissist because to everyone else they are a great person who would never be capable of such things. So they believe the lies the nar c tells about us because they can make the story so convincing that they can make you believe anything. Unless they saw with their own eyes what the narc was really like, it's easier and more realistic to them to believe that you are everything the narc is saying.