My friend got a boyfriend and now she isn’t herself

My best friend has always been a loud, free spirit type. She’s very flirtatious and a party girl. She uses drugs and alcohol and gets loud and crazy but in a fun way, not like a dysfunctional kind of way. I don’t typically do all of that but we are still good friends anyways. She started dating this boy about a month and a half ago and she doesn’t party anymore. She will go sometimes but she won’t get drunk or anything. Idk if he makes her not or what. Do you think this is a red flag?