He does sports because he wants to keep fit.
(Unless)
He felt sad when he failed the exam.( happy)

Unless he wanted to keep fit , he wouldn't do sports.
He felt happy when he passed the exam .
He didn't feel happy when he failed the exam

Unless he did sports, he wouldn't keep fit...

Unless he wanted to keep fit , he wouldn't do sports

Unless he wanted to keep fit , he wouldn't do sports
If he had passed the exam , he would have been / felt happy