firstly, you should stop talking like Parker from the Thunderbirds and then get her to write him letter telling him straight what the situation is.
he clearly feels he has some 'rights' over her and probably believed they'd get back together ... she has perhaps been a bit vague with him - thinking shes being kind, and not wanting to hurt him, but really its kept him hanging on.
if she spells it out bluntly in black and white what the situation is now, what it will never be again and what she wants him to now do, he may accept it.
but she has to spell it out to him ... no flowery phrases and beating around the bush, no 'maybe in the future we can be friends...' etc
just things like - I am with someone else now, and i am very happy - you and i are over, and i am absolutely not interested in seeing you again - i want NO romantic involvement with you EVER again.
you must leave me and my gentlemen alone and keep out of our business or i will involve the police.
she could say once 'I know this is hard for you and i dont want to hurt you at all , but i have to say this'
he probably thinks you are taking advantage of her, being forceful and she doesn't really want you... some people are funny like that
if that doesn't work, then yes definitely see the police
how old is he and her?