Slander online

Hi all, I actually can’t believe I’m writing this but my husbands ex from 15 years ago (also an old high school friend of mine prior to their relationship) has popped out of the woodwork and is spreading some very serious accusations which have no truth to them about both of us.

I was wondering what legal options I have. Facebook is not taking the posts down despite multiple reports. I want to make this woman’s pockets hurt. Please help.