Boyfriend's sister

T • Taken 01/27/19
Okay so my boyfriend's older sister "sexually matured" him at a young age. They're still close and I'm the only person he's ever told. Well, he expects me to meet her at thanksgiving. Personally I want to kick her ass and I'm worried I'm not going to be able to keep my cool around her. I hate that she's touched him where only I should've ever been. Advice please