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 =)