My step-brother doesn't like my fiance...all my life he hated me...now he won't even lemme have a say in it...

hi...i'm a 21 yr old woman. i have a step-brother and step mom. all my life i've experienced how much they hate me. mom's always discriminated against me and my step brother has always tried to bully and humiliate me. he's just a about a yr older to me. gradually as we grew up, he was kinder to me......kind of stopped talking to me altogether unless it was something very important. he has always taken everything concerning me jokingly. i don't hate him, i detest him. last week me and my boyfriend announced our plans to get married soon. dad was very happy....even mom approved. my two younger half-brothers were excited (perhaps the only 2 people to even care about me in the whole household). my step-bro was mad at me. he was dignified in front of my bf but after the whole thing was over he came down on me like lightning. he said i was making a big mistake by choosing 'that guy'. he said he's not good enough and god knows what. where is the brotherly love trickling in from suddenly??