When our relationship is going good.. he has to ruin it?

The last sentence is part of the answer. Being 17 is sometimes really annoying. But it could be that he feels a bit too much pressure, it might be from school work or may be his parents are annoying him as well. May be you just need to go and do something a bit more fun , like go for a bike ride or something that gets your lungs working and more oxygen in your blood.