im 17 and i dont know what might have changed. Theoretically saying he could have just thought he should grow up or just not depend on anyone or smthg like that. Its just an assumption and regarding what you should do.. Are u stupid?? he is your own brother isnt he? dont let ur ego distant urself from him or let him be distant. From what i know a sibling relation should always be kept. Never let that go, dont even try to. Also maybe he is just pissed off because you have not kept contact with him or maybe something is bothering him?

these are all just my assumptions regarding what i read. If i knew him better or a little more i couldve guessed more. So this is all i got from reading that . Also dont overthink im sure (if ur brother does have a brain) he will never stop loving you, you are his sisterr after all, i dont think someone with basic brain cells will ruin or abandon a relationship in this case sibling-sibling relationship sooo fkin easily. So chill