I need your advice right now.

So, my fiancé got a super random text from his sister that she wanted him to block a long time family friend just because his sister wanted to close her “chapter” of her life. My fiancé found it odd because it never happened like ever until now like what changed it. The family friend my fiancé knows for a long time like I’d say over 20 years and he used to date the sister very briefly then they remained friends until now, not anymore. We do not know what caused that. He even asked the sister why and all that. But his sister wouldn’t give him a real reason but she simply demanded him to block the family friend out of respect for her because if he doesn’t then that means he doesn’t have any respect for the sister. My fiancé doesn’t really want to block him because they are really good friends and he doesn’t want to lose that. His sister got so angry and acted super entitled that he should had block him because she’s his sister and he should had respect her wish. Is he the wrong one for refusing to block him for her or? We really need an advice. He didn’t respond back to her last text because he doesn’t know what to say at all.

*Edit*

There’s no sex assault history between her and the guy at all. They dated years and years ago. He simply wanted to know why then he can decide it for himself but she only said respect me bec I’m your family so just block him, period. Once he said no, she got so angry at him and got so mean with him. The funny thing is that she asked their mother the same thing, the mother said no and the sister respected her wish yet she gave my fiancé a hard time for that. This situation is just so weird and childish in my opinion.