Girlfriend Got My Sister In A Threesome For Our Anniversary

It was my first anniversary with my girlfriend, and I thought I'd bought her the perfect gift. It was some antique doll she'd wanted forever, which I thought was pretty ugly but hey, that's what she wanted. Not that it was a competition, but I thought there was no way her gift would beat mine. But I was so, so wrong. My girlfriend got me something I never thought I could have: my sister in bed!