contract law question?????

i bought a business from this guy and agreeing to pay him the money in monthly bases. but after a while my business went down coz of teh competition across the road. i told the guy who i bought the business from that he already knew abt this new business across the road. but he denied it. after that we come to an agrement that i only pay half the amount from the intial contract. he agreed. but now my business is doing well and he want me to pay the intial contract money. im i liabile to pay the original contract money?.

pls try to not answer me in one word answeres. coudl some1 pls help me with this clearly. thank you.

You didn't mention if you had drawn a "new" contract or had at least both signed any new agreements of the old contract.