How do I deal with my boyfriend’s sister?

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My boyfriend (Clyde) and I have been dating for ten years, and we’ve been living together for almost five years. Clyde’s biological dad (Darby) wasn’t a very good person, let alone a good dad; Clyde’s mother left Darby when she was pregnant with him. Both of Clyde’s parents got remarried and had a child with their new partner. Darby had a daughter (Dolores) whom he raised with his new wife.
Clyde was always estranged from Darby, he never called him dad, Darby never made an effort to see Clyde
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Or to keep in contact with his son. Clyde would have absolutely no relationship or contact with Darby if it weren’t for his sister Dolores.
Dolores got the short end of the stick compared to her brother because she was raised with Darby as her father figure. Darby’s most notable qualities include: apathy, selfishness, manipulation, and narcissistic tendencies. Dolores is a “diet Darby” she shares many of these negative qualities as her father, perhaps not as extreme as Darby but they’re there.
How do I deal with my boyfriend’s sister?
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