That's the practical answer - you can't market it if you can't sell it, and you can't sell it if you don't have your partner's approval.
Yes, technically, you can find a broker who doesn't care that only one party seems to want to sell, and you might get a full-price-and-terms offer and owe a brokerage fee . . . real world answer: get their approval or sit tight.
All the best,
Without knowing all the details it is hard to come up with options. An attorney could help you resolve it...hopefully amicably.
Susan Oshman, Broker Associate
Keller Williams Realty
Is there both your name and the other person's name on the deed? If the answer is yes the only way it will sell is if you both sign an offer to purchase. You, alone, will not be able to sell it with just your signature.
Let me know if you would like more options at firstname.lastname@example.org or call me at 920-988-0588