Default on unsecured loan

My son and fiancee had an unsecured loan betwwen them. She left him and not paid her share , he defaulted on payments because of this. Court action by him against her unsuccessful, now loan company is taking him to court even though he tried to make an agreement with them. Why are they taking legal action against just him , they both signed and are therefore jointly responsible. The added complication is that he works in insurance and a ccj would mean he would be asked to leave his job. Any ideas about how he can fend this off ?