What can i do about this situation?

okay so there is this guy that has done everything imaginable to destroy my whole family my marriage and other family members. his gf rides by me in friends car and harres m e by screaming profanities at me while my kids are there with me. they have startedd several rumors and now they are trying to befriend my husband when they see him out. i have asked him and his gf to stay away from my family and they wont. he seems to think his gf can do no wrong and wont believe me when i tell him she does these things. we were friends for 20 years and he threw it all away for a nasty little 19 year ld over bull crap lies and stupid accusations. what can i do to make them understand that they have to stop?