How can I get full custordy of my new born



I am a single mother who got in to a dispute with my baby’s father
I called the police on him,he tried to left the house came back with scraches on his hand,

when the police came I was questioned I what happened
he gave them a story which they bought he had scraches they said I was the abuser.

I left the house for my safety. he file a 50B and had every one looking for me.

he now has tem custordy of my new born son
and wants to to sign over legal coustody, the I can have my son most of the time.

he claims that the law will come after him for child support if he does not have full custordy.

can some one guid me in filling ?
family law would not help because my baby’s father already fill with them and I have no money for a lawer