1) Adulterous 2) Extramarital 3) Illicit 4) Outside 
[adj] - outside the regular academic curriculum 2. [adj] - outside the regular duties of your job or profession
adjective outside the regular duties of your job or profession
outside the regular curriculum or program of courses: football, orchestra, and other extracurricular activities. · outside one's regular work, responsibilities, or routine. · outside the conventional bounds of propriety or ethics: Does his wife know he has an extracurricular girlfriend?