Divorce & taxes! We owe...so it's off to work I go. 

Our divorce isn't final yet.  He went to a tax professional assuming we would file joint returns.  We owe $7000 in state & federal.  So, I went to my own tax professional to compare how much I would owe if filed separetly.  I found out I would get back what I paid in taxes last year & he would owe about $15,000.  That's with him claiming our two kids.  He made significantly more than I made in 2007.  $110,000 compared to my measly $11,000. 

Question: if I file seperately can I still be liable for his tax bill?  Since I benefited from the marital income in 2007 he is saying I would still have to pay half of the $15,000.  If that's the case I may as well sign the joint return & save us both some money.  He just won't agree to pay the whole $7000.