It's a little bit complicated and based on an old English concept called, "Tenancy by the Entireties," but in simple terms, remember that all property acquired while you're still married is marital property. So, if you buy a house while you're still married, the house is marital property. Title companies, banks, and mortgage companies want to make sure he acknowledges that the house is marital property. It's usually best to wait until after you're divorced to make major property purchases.
The contents of this answer should be considered friendly advice, not legal advice (I'm a pretty friendly guy), and the answer should not be construed to constitute an attorney-client relationship. If you'd like actual legal advice, call me for a free consultation at 813-635-0222. Also, if you liked this answer as much as my big ego thinks you did, be sure to click the thumbs-up button!
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.