If he's sending the stuff TO YOU-and you've told him not to do this before, you can indeed file charges over it-or at least go to the police.-it doesn't matter "who's ex" it is.But-in the meantime-can you block his email accounts-or have yours changed?Charges are actually rare in harassment cases;most times the police go and talk to the person doing it and they get the idea they better stop of they will face charges the next time they do it.This is usually enough to stop about 99% of them.The police will ask you though,if either or both of you have ever told him ,upfront and clearly that neither of you wants anymore contact with him-EVER;this means breaking all ties to him,and blocking him from social network sites like facebook;people frequently leave the "Exes" on there under the guise "I just want to know that he or she is OK"(which is a rationalization- the fact is people want to know what their ex is up to "romantically")
Essentially,depending on what state you live in-what he's doing,with posting pics and phone numbers PRETENDING to be your GF- COULD be not only considered harassment ,but could also be considered to be ;identity theft or criminal misrepresentation,false personation or some other similar charge according to your state's definition.I'm sure the guy thinks he's being pretty smart by doing this-but he's hardly the first to pull crap like this and chances are your local police have heard of this kind of thing a hundred times before.
No site will provide you with the IP addresses of the users-privacy policies on the sites say that and they will only divulge that information to law enforcement,even if you had the IP addys you couldn't do much with them-you'd have to have the IP traced to an individual account through the ISP-who,again-can't give out that info because of privacy law and will only provide it to law enforcement.
He's not going to "break you up",no matter what he does, unless you (two )let him.He doesn't own either or both of you after all-what he's doing are things that he thinks would cause HIM to break up with someone;..in other words-if she was still his GF and someone else was doing this to him,he would blame HER for it...if you want to play along with his game that's up to the two of you.
Im not sure what the family/life/work situation is here in this case-or what contact with him ,if any is really "necessary"-if your GF had kids and hes the father (with visitation rights) then inevitably they have to stay in touch with each other-but otherwise leaving "strings attached" is unhealthy for everyone involved.