Hi I have a girlfriend who is still married but is separated from her husband the night he left she got a call from a friend of hers saying that her husband packed all his and her son's stuff and left we have found out that he is in Indiana but not for sure where in Indiana the only contact he gives her with her son is restricted phone calls but my question is if she was the sole provider out of the two she was working and he was not and he just took off with her son to be with a another woman and has been gone for five months does she have the right to just go up there and get her son?

Did she have a court ordered custody agreement that made her the custodial parent? Unless she did... there is nothing she can do.

But I will assume she did. And if she did... she should contact the court... as well as the police.

He didn't have to right to take off with THEIR son, and she doesn't have to right now to go there and take THEIR son. Who was providing has no bearing.
She can press charges with the police and she should file for divorce. Going there alone may spell trouble.

Wait, she wants to go there and get their son? First you said just somewhere in Indiana..
Does she know where they are or not?