How can we get rid of ex husband?

I am very concerned about my life and my wife her ex been coming back to her back and forth and wont leave her go on with her life he makes wrong umptions about her and hire other people to get to know her and ruin our life he tells her she is abused and so ever but the truth is he is abused mentally and emotionally he was ignored by his mom and she was never there for him same with his dad he was so cheap to his son and his ex wife -which now my wife- didn't help them out and told them to deal with their life by themselves so they couldn't get married because they were very young about 19yrs old but somehow they maneged themselves but still she couldn't go on with him cause his parents didn't leave them alone and treated her very badly so she couldn't take them anymore cause they always controlled him and he had no saying so she married me and left him but since then him and his family still don't leave her and don't stop chasing her and keeps stalking her and haring her now that they lost her they want her back so he been pretending all this years that he is the father of our child. I mean she got pregnant from me but he keeps saying that its his child i told my wife so many times to ignore him cause he is crazy and she shouldn't blame him for what his parents put him through i mean last time he came after her wanting her back we heard his wife got pregnant then we found out that she got pregnant during him wanting my wife back again so my wife should ume that's her child that his wife gave birth to at that time. (chuckle) I know her ex husband very well and my wife told me everything about him he tells her that she sneaks behind my back while i can see my wife talking to him or talking to others in front of me and dosen't have to neak around but it's him who been sneaking behind his wife and fooling around with other woman and hide everything from her and keeps it a secret. Couple of month ago he wanted my wife back i told my wife it's really up to her but it was cause of his parents or he wasn't man enough to keep her at that time so, she tried to give him a chance to trust him which she always did then, we might get a divorce after that so she can go back to him until she found out his wife is pregnant and hide it from her and lied to her telling her he is divorced. He kept telling her there is no way now you wanna be with somebody else but then he cheats on her and slept with his wife so, she started to hate him and now she can't trust him anymore cause she tells me once a lier always a lier and once a cheater always a cheater. But, I need help now and i want him to stop cause she dosen't want to have anything to do with him anymore and don't want him to be there for her why can't he understand that she dosen't want to be even his friend cause everytime she gave him a chance he end up to hurt her so she dosen't think he can be trusted anymore he is nothing but a lier and a cheater. Help Please all he wants to do is to ruin our life just because he is rich dosen't mean he can get what he wants and control other peoples life.