My former employer issued me a credit card to use (in my name) for dinner/drinks with clients, to use personally for gas and other things. He always said is was OK and he never once asked that I pay for any of these charges because it was a part of our business and he felt badly because he couldn't always pay me on time. The business began to struggle and I eventually ended up leaving. He is now coming back to me and saying that I owe for charges/purchases I made on the card while still employed.

Does he have any recourse and I am I help responsible for these charges?

Unless there was something written about the terms by which you could use the card, I doubt if he will win. You will need to document things to show the judge that you used the card in the performance of your duties as an employee. If you can do so, he will most likely lose.

I'm afraid you may have been misled by your former employer. He can't just hand you a credit card and tell you to charge whatever you want for your own personal use - that would be considered income to you and should be properly taxed. If you used it for business purposes he would need receipts in order to justify the expenditures to the IRS. So it sounds to me like he has just learned the error of his ways, and his only recourse to get receipts from you, and if you can't provide them insist on restitution. Assuming you don't have receipts - if I were you I would respond back to him in writing that all charges on the card were for legitimate business purposes which he approved at the time.