Rocky relationship

I am 17. i have been dating this guy for almost 2 years. we trust eachother completely and everyone says we have the perfect relationship. but lately, within the last few months, things have changed. Now it's like 60% of the time he is the amazing guy i fell in love with, and the rest of the time he is someone else- cold, distant, uncaring. he seems to care less in general. i have talked to him and he apologized and said he hasnt been sleeping...it got better for a couple of days but now it is back to the way it was. i know we are young. but both of us have been through a lot and he is the only one who ubderstands and i trust and love him so much. i dont want to just break up. but i'm not sure what to do now. SOS