I would probably re evaluate my social group. If they are spreading lies about you that can hurt your reputation then they are most likely the more dominate figure in your social group. I would say its time to find another group of friends. The most stable way to transition out of a relationship is for your S/0 to have no original ties to your social group. That way you have a healthy support network if something is to go wrong. It is possible for them to tant that network or maybe perhaps you are the tanter but its very rare. Either that or you made the age old mistake of seeing a friend in the social group thus disturbing the balance.

I'd probably start with taking a good, long, hard look at MYSELF to be sure that they ARE lies and that I am NOT as is being said! You'd be amazed at what you'll see when you honestly look within..or if you keep a journal...oy...the times I've had to call my own self to account (what the hell am I doing...over and over here!!!!! "dumbass!") lol If they ARE truly lies...you're golden, because any so called REAL friends will know they are lies, because they know YOU. If there is a grain of truth to the stories...even a tiny little grain...then you decide if you do not LIKE those qualities in yourself...and decide to change some things! If you are above reproach in your character, DO NOT buy into the ex's bullchit! Do not cause a stink, do not go out of your way to bad mouth the ex. "Yeah, I don't know what his/her problem IS. He/she is annoying, but I suppose he/she has to justify the break up somehow, know what I mean?" If YOUR friends are really your friends (and it would be helpful if they are MATURE in nature as well) they will not be interested in listening to your ex. They will likely suggest that the ex go sell crazy someplace else, or will ignore the comments, or tell the ex..something like, "Well, I don't agree, and I'd rather not listen to this drivel, if you don't mind." If they seem to delight in sharing mean spirited dialog they've heard WITH YOU...I would question the level of their friendship in the first place. We all need someone to vent with (most of the time) when there is a break up...however, unless there was actual abuse in the relationship I would never bother to discuss the failings of it with "everyone" WE knew...what's the point to that sort of garbage? Rise above it...and enjoy being a wonderful person...that way you'll attract someone else wonderful to enjoy knowing!

confront your ex.

I possess enough integrity to know that I can stand tall in the spread of lies.

You can't have much of a reputation to being with, if an ex is all it takes to make others doubt you. Lies are by their very nature, bound to perish when faced with the truth. Unless she is being libelous (in which case, take her to court) you need only present the facts to counter her lies. In which case, she'll lose credibility and you'll earn respect.