Can I sue Facebook due to them refusing to remove a person stealing my pictures and starting relationships with different men. I have proof due to one of her boyfriends stumbling across my REAL Facebook account.
What is the name of your state?
If the person posing as you has taken photos from your account to use on her own, you can file a DMCA takedown notice with Facebook, claiming copyright infringement. Facebook will remove your photos from the person's Facebook page. From there, file a complaint with Facebook.
If your reputation has been demonstrably harmed by her use of identity, you can consult with an attorney in your area to discuss the wisdom of filing a defamation claim against her.
You can reread the terms and conditions of Facebook at
https://m.facebook.com/terms.php. Facebook is immune from suit for content posted by others, through the Communications Decency Act's section 230.
Any lawsuit you consider, or any criminal action taken, will be against the person impersonating you - not Facebook.