This is the reason I don't have a Facebook page anymore. I had a guy who I thought was a friend of mine come right out and ask me to sleep with him. When I rejected his advances, he got on Facebook and began a rant about how horrible it is to have someone who you thought was a friend abandon you. He turned the whole situation around on me and made me look like the bad guy while he made himself look like the victim. He pretty much ruined social media for me.
A lot of friends are not really friends and will mock you secretly and/or they have friends who are your enemies and they do the same. Also, as you mentioned, some get on there and rant about romantic things - stuff that is personal which do a lot of damage and really nobody's business.
I don't let stuff like this get to me. I added a friend from high school, and I got into an argument with one of his stupid dumbass friends, who I happen to know, too. And not only does he unfriend me, he sides with the other guy. I've always been nice to him, but such is ignorance. It made me realize he was never a friend of mine. I tried to go to Wrestlemania 2 years ago with him, only to learn that he doesn't like wrestling anymore. Which isn't farfetched because WWE isn't what it used to be anymore, but that removes the one connection we had.
I bumped into him a while ago during a local festival (the city is a "small world" kind of thing), no feelings towards being a friend of him again, I just waltz past him.
You just gotta look out for what's going on when it concerns you. Just dump the friend and never look back. Those who have your back, by trying to be a friend of yours and not just another number increase for your facebook - are the ones you need to pay attention to.
Oh, and by the way, smearing another person in public on social media is also costly, so I don't advise anyone to smear another person without a reason, or whatever. Someone tried to smear me on twitter, and I fought back. He eventually stopped.
Someone can sue you for smearing another person in public, and
WIN. All you need to do is gather all the evidence towards the other person, and be careful with what you're saying.