Don't take any money from your ex until after you are officially divorced with a final judgement of divorce signed by a judge.

Depending on the state, it could be viewed as an attempt to reconcile and delay your divorce proceedings. This happened to a friend of mine in Massachusetts.

The tax filing and splitting refund is not the same as him giving you his cash, no matter how he gets the cash. Splitting a tax refund or him paying any tax owed would not affect your proceedings.