Witnessing sibling under influence

On a ride back from a party with my brother and his friends, my brother got drunk and started hugging me and being weirdly loving when he usually isn’t, I also witnessed him on Molly which was weird because he was being loving and protective, he told me while he was drunk he feels like when he’s under the influence he’s him self the most and he told me that isn’t good but it’s true apparently, he also started making out with his gagging drunk best girl friend, it was so fucking weird, I was kinda in shock. The person driving however was 100% sober, idk if this is normal or normal for me to experience is this gonna increase my ptsd, they’re all 19 btw and I’m 16 maybe it’s not a good idea to chill with them, I’m just gonna make friends with people 16/17 I realized I’m not ready to be around that chaos