Hello, it's good to hear from you.
The best way to address your ex's smear campaign can be broken down into two actions- how you behave with others and what you say to them about the topic.
First, it may be difficult for you in your shared social circles for a while until your friends and acquaintances figure out your reaction to what your ex said about you. What you need to do is decide your reaction ahead of time so when you are confronted with what your ex said or you just need to interact with your shared friends and acquaintances, you already have thought through and practiced if need be what you want your reaction to be. Smiling, being gracious and bringing up how others are doing helps a lot. Although it is ok to be upset by what he did
, you don't want to show them everything. Don't mention the topic and do your best to act as if it didn't happen. Let your friends and acquaintances bring it up if they feel the need to.
The second thing is what you say in response to what your ex said, especially if it is brought up to you. Along with your behavior, you want to be able to answer anyone who comes to you and confronts you or even just mentions your ex's comments about you. It helps to adopt an attitude that you are hurt by it rather than start defending yourself (although that is a natural response for anyone). For example, you can decide that you may want to respond by saying "I'm really sorry he said those things and I feel bad you were exposed to such lies." By saying something like this, you can acknowledge you understand the situation and how hurtful it was to everyone but that you want to move on. You also minimize it and even reduce it's impact by calling what he did lying. That helps this to be easily dismissed by others as not important.
If you are very close with some of these people and can trust them, ask for their help in telling others that what your ex did was just to hurt you and that none of it was the truth. By having others do this for you, it helps show that you are right and your ex was wrong.