When you feel that your trust has been violated it can particularly hurt. Just as this is the case around infidelity and everyone acknowledges this, it is also the case around lying. While people speak of the spiritual benefits of forgiving, Schultz and other researchers have identified physical and mental benefits from forgiving the one who has wronged you. Forgiveness is important to you whether or not you decide to move forward with the relationship.
Understand What Forgiveness Is and Isn't
Forgiveness is about letting go of the anger and negative emotions that you have towards the one who has wronged you, in this case by lying to you. It is about creating a new start emotionally, whether or not you continue in the relationship. When you forgive someone, you are not saying that what they have done is right or even okay. You may still hold on to having them brought to justice or other consequences because of what they have done. The real focus in forgiveness is on your ability to move past the negative feelings and the anger that would continue to eat away at you.
Consider the Context of the Lie
In the case of a lie, it is important to consider what prompted the person to lie to you. Consider whether what this person said really qualifies as a lie or if it was only false information that he believed to be true at the time. Consider also how serious the lie was, in terms of how far from the truth it was, how significant the thing lied about was or in terms of patterns of lies. You may additionally consider the other person's intent, for example if they were lying to try and protect you. The context of the lie may give a perspective where it is easier to set aside the feelings you are having.
Reflect on Forgiveness You Have Recieved
As you move towards forgiving the one who has lied to you, it can be helpful to remember when you have been forgiven. Honestly reflect on your own past in and out of this relationship. Think about the events that have surrounded those times and what it meant to need, get and/or not get forgiveness. If your spiritual or religious tradition talks about forgiveness, especially about you being forgiven, reconnect with that part of your tradition. Looking at the way that God (or other higher power) has forgiven humans, including yourself, along with the way other humans have forgiven each other can give you strength and ideas to be able to forgive the one who lied to you.
Forgive the One Who Wronged You for Both Your Sakes
The anger and other emotions that you are holding on to before you forgive are affecting you probably in ways making you be someone different than the person you want to be. If you do not forgive the person who lied to you, that person's lie(s) will continue to have power over you and will continue to influence you. You deserve to reclaim the control over your life and your emotions. In doing so, you may chose to forget what happened, but you don't have to. What you need to do is not allow the negative impact to remain your focus continually drawing you in. Focus on why you need to move forward and immerse yourself in your future.