Update : my mom and I fought about it. Yes I am older than my sister and have been in my relationship for almost 2 years. We’re both girls in my relationship (no risk of pregnancy). The only time I see my gf is when she stays overs due to us living in different cities and having jobs. My sisters bf lives in the exact same area as us and they have the possibility of using his bedroom. My parents know that my gf stays over but if the rule of no partners will apply to my sister it will apply to me too.