My son has not been allow to see his son after the baby mother broke up with him we live in new york she lives in jersey city he wants to see his son

the babys mother broke it off she won t let him see the baby i need help with this his son is three they lived together up until july 2014 i cared for the baby for 14 mths in my home he is disabled my son is 23yrs he wants visitation of his son he is angry because the mother left him for some else and won t let him see the baby but then calls him to tell him what the other man is saying i feel like she wants to move on but she does not want him in the childs life she is calling him telling him he has no rights i wan my son to be in his sons life he is a good dad from day one i wanted to get a lawyer for him so this can be handled right does it cost alot