coulple broke up 2nd morgage almost paid off

We've been paying over the minimum on 2nd mortgage for some time. At this rate it would be paid at the end of year. Ex can't afford to keep up extra payment. I am still living in house, not ready to sell. Should I continue to pay extra to pay off 2nd mortgage?? Is it better to pay it off or add to bill for ex when we do sell or I possibly buy him out?