No way would I be getting a second on the house to fund his irresponsible behavior with money while he’s threatening divorce!!!

Why was there such a large tax bill? Is he self employed and not making the correct quarterly estimated payments? What did he spend the bonus on? What’s he been spending the credit cards on?

This degree of financial dysfunction usually suggests one of a few things:
1) Living beyond your means. (Some men hide this by building up credit card debt while maintaining the illusion that he’s bringing in enough income)
2) Spending on addictions like drugs, gambling, porn, or mistresses. Too many here have discovered too late that a large chunk of income was going to these things.

I suggest you make the financial choices that are best for you if you divorce. That may or may not happen but you need to protect yourself if it does. Try to find some way to begin paying the taxes without refinancing the house if you can. Take over the finances or at least insist on sitting down for a monthly budget meeting. You can present it as necessary to clean up the tax debt before you can afford to divorce. Discuss anyplace you can tighten the budget.

Can either of you pick up a small side hustle to bring in more money? Short-term pain to pay down the tax debt could pay off big time in the future. (Don’t start paying down his credit cards until you find out how much you are responsible for).