Is it possible to rebuild a relationship?

Even after lies? Is it possible to help the person move on form the past? If so, what could one say or do?

Trust is absolutely essential in any relationship be it friendship or romantic. No trust equals a lost cause. Both people must be considerate of each others feelings and boundaries. I once had a friend who I trusted and he ended up smashing it all to pieces and he kept doing it over and over as I kept giving him chances. Some people deserve second chances depending on the circumstances on a case by case basis but if things go back to square one the second time around then don't look back and throw in the towel. Make sure you express it very clearly to them why you're doing what you're doing because sometimes it takes people a good knocking in the head to figure it out the hard way.

If there was something you could say or do that could magically replace trust, I'm sure the world would be a better place. There is no way to trick somebody into trusting you again. Seeing where things went wrong and taking responsibility for the things you do wrong is the first step. Working on yourself and instilling the things you learned into your every day life will help you improve and become a better person, to the point where it's genuine and they know you have changed. It's exhibited.

Forgiveness is good but only when the person deserves it. If it was a spontaneous mistake that they made, you should forgive them. If however there was a pattern to it, there is a very good chance that it will continue for ever and you should not try to peace things out.