Quick Qhestion about Divorce and Taxes.?

I filed my federal taxes, husband and I have been separated since March last year and going through divorce now and I started working the month we separated. So all of my income I made and took care of our child and she was with me more than him that year. My lawyer said I should not have filed them and his lawyer is going to try and force me to amend them so we can file jointly and split it. I do not see how this is fair and honest since he is living with his girlfriend and she is pregnant. Does state divorce laws trump federal tax laws? cause i need this money to pay my parents back for paying for my lawyer and to buy a car :(