Am I resposible for paying a bokers commission if I close?

Not necessarily.  Closing the business may not be the same as taking it off the market, as I assume that  you would still be willing to sell even after you close the business.  The issue would be whether by closing the business, and thereore making it more difficult to sell, certainly for the same price, you violated your obligation of good faith and fair dealing under the contract.  Another question could be whether the provision that you have to pay the full commission is a penalty, rather than a valid liquidated damages provision, which it may be.  I believe the true measure of the broker's damage, assuming that closing the business constitutes a breach, would be the amount of the commission minus the expenses the broker saved by not marketing the property after you closed it.  The damages might even be zero, if you can show that, even if you hadn't closed the business, it would never have sold before the end of the term, and the broker would never have earned the commission.