visitation and custody?

my 8 yr old sons dad has threatened to take my son from me...i mean to live with him. (we live 10 min apart) he wants to get custody of him and has said he will do whatever it takes ( have it on text) to get my son. He also threatened to come in between me and my BF if he has to. He is now telling my son that he can come over whenever he wants..I dont know where to go first. He is very manipulative and contorling

Update: he also said that He doesn't need me to take care of my son. He can do it and it's best for my son that way. What do I do? Who do i contact first/