Making separation agreement null and void?

My husband and I separated several months ago; we signed a separation agreement, which was notarized and filed with the court in the proper manner. He signed it of his own free will, etc. I am seeking the divorce because he was abusive, an alcoholic and a liar; his take on our marriage is different. There were no allegations of adultery at the time of the separation agreement being signed; he is now accusing me of adultery months after the fact and supposedly has some sort of evidence. I refinanced my home and he signed a quitclaim, again of his own volition. I agreed to pay him a settlement of $26,000 to be divided into 3 parts; I have already paid him $15,000 and the remaining $11,000 is to be paid by August 2012, per the separation agreement that we both signed and had notarized and filed. He called and demanded the rest of the money now based on the fact that I supposedly cheated on him. He says “my attorney” says I can have the separation agreement changed and “take your house away from you” because of adultery. Does this sound like something that can be done? Do I need to consult an attorney again?

Unless the separation agreement contained language to allow for this in the case of adultery then he probably can’t do what he’s threatened.