Ex not paying his part of mortgage

[Elizabeth White]

Hello everyone, i am new here and I want to discuss my problem with you. 2 years back me and my husband took a loan for some personal reasons. It was taken jointly since both of us are working. It is a fixed rate loan for 7 years. 

Last year we got divorced, and till February everything was fine, both of us were paying the loan. But from March my ex stopped paying his part of the mortgage. He gave some excuse about his brothers illness and asked me to pay for 2 months. I did as he told but now even after 4months he hasn't started paying it. I can't afford to pay the full amount each month. What should I do?