I am being threatened by my ex. Help?

I am being threatened by my daughter's father. We have been split for about 5 years not married,on and off a little. I am recently in a new relationship and I am very happy. My ex does not want any other man around our child and is very angry. I am nervous that he'll try and do something about it. He has family that I guess all i can say are very dangerous and I would'nt hold anything against them... Can I please have some advise. I really dont want to spend my life alone because of him, and I dont want him out of my daughters life because they both really love each other Help!