if you are the liar, then it's too late to take an action, but if she is the liar, you will never understand untill she says. So if she says she is the liar, then again it's too late. Find a better for you. or tell her never lie again )) may work

I would find out why she lied to me. But beforehand, promise her that I won't be mad or do anything crazy. Because basically I am just curious and want to know. What's done is done, and I would tell her that it's ok to tell me the truth in the future.

Well if it was me,id confront them and ask them why they lied to me,and what they lied about. If it was to stop me from being hurt,i'd understand,but it if was just a bad lie,id think about leaving. Ive been there,lied to about me my ex girlfriends feelings,then she dumps me when she knows i had feelings for her,so its not good to lie. Id never lie to my partner,i have respect =)

I agree with jura ..

Ask them/ email them as to why they are telling lies. If the relationship is strong enough to be open and for each person to tell the truth, it will survive and become stronger.