You cannot check someone elses credit record on your own. The only way to do that would be for the person to order his own credit report and allow you to see it. The laws are pretty strict on this issue.
In my experience, my AH had a joint credit card with his ex-wife. In the divorce it was stated that she would keep the debt. Needless to say, she defaulted and it adversly affected my husbands credit. When it came time for us to buy a house, I called the creditor and discussed the issue with them. They told me that it didn't matter what the divorce decree stated. His name was on the account and he was responsible for the balance. On the brighter side, they did agree to a settlement amount which was less than the balance, which we paid. I hope you hear better news. Good luck.