sorry you are going through this. it is extremely difficult. i would delete the whole FB thing. i know, i know, people here may think me silly for how often i advise that one single thing. but i must tell you--it did wonders for me. not only was my ex there but so were all the mutual friends/aquaintances/family on both sides...on and on. even with the "block" or "unfriend" options things could just creep in from a place unexpected. whatever crept in was no good for me to move on in a good, solid way. there is life outside of FB, after all. just a suggestion. doesn't work for all.
other thing is, warning others generally backfires. we aren't with them anymore and have to let it go. remember they are manipulative so anything you say, do or attempt to do--no matter how or why you do it--it will be turned on you. you don't need that. it keeps you in it when you do not want to be. also makes it look like you are still hanging on.
prayers