Sick of the fights

It has been 2 days since the last time I spoke to my lil brother who is only 18. It seems that along the way from middle school and now we have just gotten farther apart. I remember a time when we use to do things together & just be able to talk without getting into fights. But now we just dont get along. I sometimes have to play dad cuz he seems to walk all over my mom. And I wish I didn't but the things that he do makes me have to jump up a& put him in his place. But I know in reality that the only person that has ever been able to keep that boy in check was my dad. On Sunday we got into another one of our fights where he again took it to far and even laughing while i cried. As he was doing that I told him that he was sick. From there I wrote him a letter stating all my feelings. He has yet to talk to me about the letter. So for the most part we are in non speaking terms. Hopefully, he comes to realize that he needs to stop being so angry and start living and being such a heatful person cuz if he's not careful it could comsume him in the worst possible way.