You're not obligated to keep an ex as a friend on fb at all. She is an ex, so your cutting off communication is completely understandable and you're not doing anything wrong by unfriending her. It's YOUR facebook! You choose who is your friend there or not. For me, I've kept my ex on there for the moment because we are separated and not yet divorced but.. thats only to keep her from badgering me about why I unfriended her (she thinks we are friends still, and really I only keep in touch b/c of the kids). that being said, I've made it so she doesn't see my posts and comments and I turned off the feed from her so it's like she's not there anyway. Try that if you are uneasy about unfriending her.