Family is falling apart and my mom blames me

My mom has always treated me and my 16 year old brother differently. I have to get straight A's or I'm grounded. My brother is failing almost everything and she doesn't care. She was always more relaxed with him but with me nope. I have to do everything right the first time. I graduate High school 3rd in my class and I start college in August. She was yelling at me for not being 1st and I snapped and told her how different she treats me and my brother. He's allowed to fail everything and mess up but I make a tiny mistake and I'm grounded for a month. I called my mom misogynistic and she rolled her eyes and said "Oh plz. Gender has nothing to do with it. I'm harder on you because you're actually smart and Adam is stupid so there's no point being hard on him. If I keep my expectations low with him I can't be disappointed! You're going to college. He will probably be living with me until I die." As we are fighting my brother comes down stairs and says "So you lied to me when you said people were wrong about me being stupid!" My mom froze looking stupid and didn't say anything. He asked her if that's really what she thought about him. Again she said nothing. So he starts crying and saying "Fine! You won't have to worry about me living here until you die since I'm so stupid!" And he left. My mom called our dad because she thought maybe he ran away there but he didn't. And now she's saying this is all my fault. My brother has been gone for 6 hours and my mom told me since this is my fault I need to take my car and look for him. I told her SHE caused this mess SHE can find him.