Should i take pay for laptop mywelf to keep from ruining credit?

Five yrs ago I wanted a motorcycle. So she agreedw to co sign for me. I made sure I made every payment on time for five yrs. About three yrs back she met a guy who I don't like,but its not my life . Any way she marries him he ruins her credit.so now she needed my help to get a computer.I said ok ,when she first got it . It was only 600 now its1500 after three yrs and its ruining my credit . I dnt want it.cause I'm saving for my own.I confronted them about three mos ago . They promised to pay 300 for the next 5 mos til it was paid they lied to my face . I past the point of mad where I'm not even mad it jus want it paid .for the last two mos they paid it on time . But the rest of the time,nope. The only reason it went on that ling is because I got hit in the recession. Now that I am able to pay should not even say anything to them to just pay it and call it a day? I know for sure it will be a cold day in hell before financally help her with anything again. I'm am literally curing back on everything to get my credit cards paid off. The bill wad only 40 a month .they act like its nothing. What should do different because I kno the only it getting is when I pay it off ,but what would you do???