What can i do to help my brother?

My brother and I have always been rough with each other (Hes 14 and im 16). When we were small he used to love me soo so SO much. he would always want to play with me and always be so nice, bring food for me even though we fought a lot. i admit i was not the nicest of sisters. i was very bossy but i loved him so much and made that clear. then throughout my preteen years (13-15) we started getting worse, mostly because of me i admit. i was going through hard times - bullying in school - so when i came home id be in a bad mood and hed be annoying and rude and id just explode and wed fight. but then things werent so bad. we were fighting OCCASIONALLY and wed always immediately make up afterwards. But this year, has honestly been the worst of my life. Hes changed so much.. like a 180 turn. At first i kindof understood: new school/new system/having a hard time adapting/not making friends + adolescence so i tried my best to be understanding. But its been getting so unbelievably bad. Hes SO RUDE to my mum. As in sometimes leaving me open mouthed from the horrible things he says. and hes a million times worse to me. He says horrible horrible things and is so angry all the time. ive tried everything from trying to be nice to exploding back at him. weve had the worst fights ever and when i try to talk to him about anything he just retorts with rude comments and anger. im no angel i have a short temper too so i usually just tell him to get lost. But i mean throughout our whole lives we always had that deep connection. the kind of brother sister: we fight on the outside but on the inside we love and care for eachother. but im not overexaggerating when i say i dont think thats there at all anymore. when he was 12 i told him i hated him and i found him crying in his room (we made up after and i apologised etc) but i mean thats how much he loved me. now its nothing..its worse than nothing, he hates me, he hates life, he hates EVERYTHING. i really dont want him to be angry all the time. i want him to be like he was. my mum used to call him "white heart" because he had such a pure loving caring heart..now its like theres so much hate there and i dont know why. i know im partly to blame, but hes never been like this before. weve always had ups and downs i just dont understand why hes being like this now. weve had countless talks, my mum cant take it anymore. shes getting more tired every day and im really worried about her. she cant handle the rudeness and anger thats my brother and shes always crying. i dont know what to do. can someone please help me