My Very Own Bisexual Girlfriend

I’ve been dating a girl who’s bisexual for almost two months now. I’m crazy about her, everything’s clicking, and a few days ago, we officially declared ourselves exclusive. Only problem is we haven’t exactly discussed any “ground rules” – if there are any to be made – covering her bisexuality. I know it goes well beyond some experimental phase and that she’ll always be very attracted to women. I’m okay with that and I certainly wouldn’t want to limit her or deprive her of something that she innately desires, and that I could never physically provide for her myself. But at the same time, I’ve never been in a relationship where other people are fair game, and I have no idea how I’d react to such a situation. Part of me says, hey, it’s just chicks, and that’s always hot, and the other says, um, why can’t I be enough? It’s a tough situation to hash out on my own. Care to help a brother out?