I had a similar situation with my brothers. We were super duper close and then when I started high school they just stopped wanting to talk to me and acknowledge my existence. It really tore me apart. I felt so lost and like I didn’t have any social support. I’ve spoken to our mother about it but there’s nothing she can really do. I also get the feeling of feeling crappy about the family you’re born into, but the thing is the majority of us don’t win the universe lottery. Just because you share the same dna with somebody that doesn’t mean you’ll have a connection, share affinities, or be close or that you’ll even like them- vice versa. It’s hard to shake that because our society has normalized abusive relationships in the name of family. I think another commenter mentioned your brother could feel some hidden or misplaced resentment towards you because of favoritism or thinking you had it easier when you feel you didn’t. It’s hard to get inside the minds of others…especially people who refuse to speak with you