Advice on having my gf in my band?

My band needs a singer, and my girl friend is really good at singing. I asked her if she wanted to be in my band. She said maybe. I've been so stoked about it that i told my older brother. He was all like "you better be careful, and think about it," and i was like "why." At first he wouldn't tell me why, but then I got him to. He was trying to say things like if there was ever a problem in our band it might affect me and my girl friend's relationship. I think he's wrong. I think he's just trying to make me sweat it and trying to mess with me. Any advice? Any help would be appreciated.