Check with your attorney and a father's right's group on this, but it seems to me, if you are being asked to pay more than you make, then the overage should be paid out of assets that would likely be split in the divorce - thus decreasing your ultimate liability by half, no? For instance - if she would be likely to get half of your 401 K, spending that down to cover these expenses would decrease what she would get. Better yet would be to spend down other savings. Worst would be to put it into debt in your own name - debt that might be claimed as "yours alone" since you acrued it after the separation.
