My boyfriend and I have a 3 month old son. My boyfriend abuses me and threatened to kill me. If I call the cops they will call DCFS. Will I get my son taken from me?

It would not seem likely the police would take your son away from you, given what you stated here. If the police have suspicions, they may remove the child to a temporary placement. But if you are telling the truth here, the police would see that you and your son are taken to safety.

You do not have to wait until the next time this boyfriend starts beating on you - call and report him. Make the complaint and file charges. Get to safety before he has the opportunity to hurt you again.