How to deal with bf's sister always hanging out with us?

I am glad my boyfriend is family oriented and I even like hanging out with his sister. It just seems like the closer I got to my boyfriend, the more she hangs around a lot.

Whenever I'm with him, she's always there and it's the three of us. Sometimes she'll bring her long term boyfriend around but she seems to always want to be around us more. I just don't like feeling like the relationship involves us 3.

When we go out my boyfriend usually invites her too. Our weekends usually consist of hanging with her or her and her boyfriend. I feel like he'd be offended if I asked to cut down on her spending time with us.
How to deal with bf's sister always hanging out with us?
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