<human>: I've been with my GF for two weeks, so it's still pretty new, even though we've dated for about 5 months.

Later this month, we are going to my brother's birthday party and my new GF is meeting my brother and his GF for the first time. Before they started dating, his GF and I slept together a couple of times. No emotions involved and no strings attached, and after those couple of times it had just kind of run its course. A few months later, my brother and her kind of fell for each other (we all knew each other before all this started). My brother knew about the history between us before going into the relationship. It was a little weird at first, but now all of us are perfectly fine with it. I see them rather often, and there's no sexual tension or that kind of thing between me and his GF at all.

So here's the question: Should I tell my new GF about this before we meet them? Should I wait until after? Or shouldn't I tell her at all? I believe in honesty, so I'm inclined to tell her about it. I'm just not sure how to go about it.

Can you condense the text into three sentences or less?
<bot>: I slept with my brothers GF before they started dating. Now my new GF is meeting my brother and his GF for the first time. Should I tell her about it?