Hai.I'm pregnant now for 4 months and the father scape is responsibilities and goes with other girl.now I would like to ask if I can file a case against him and how much monthly support he can give us with our child.

First at least in the US, you can not file anything now, after the child is born you can file for custody of the child and for child support. At this point you can no file anything.

You don't have a child yet, therefore you have nothing to support. Once the child is born you can file for support, until then he isn't responsible for anything.