Advice...

So my husband has this friend who always has to run his mouth about me and put me down. He even went as far as to say that my husband wasnt the father of my kids. And he's always saying negative things like that. He's trying to turn my husband against me but my husband doesnt see it and wont stop talking to the guy. Its putting a lot of stress on our relationship and Idk what to do? Im not perfect and I dont want this guy bringing up my flaws all the time and putting me down. But hubby overlooks what he says. What can I do?