so i think their relationship would be an open secret, so almost everyone of the trojan royal family knows or at least suspects something, maybe through gossip because someone saw them or because the siblings cassandra grew up with know how she acts around someone she likes, but everyone pretty much tries to ignore it, because there’s a war going on, and at that point people have to worry about other things than who helen fucks.

the first ones who suspect what’s going on between helen and cassandra would probably be helenus and hector because they both know cassandra very well (i like to imagine that hector and cassandra were very close as children and teenagers but grew apart because of her prophecies and the war).

what i think would be very interesting to explore is paris’ reaction, because he thinks to be with helen is his right and his right only. and he probably thinks that helen is in love with him and only him because he refuses to accept anything else. so a scene that i like to imagine is that when hector and paris have a fight, could be something completely trivial, and hector says something along the lines of “well at least my wife loves me and doesn’t fuck my sister” and paris is totally perplexed because he didn’t even think about the possibility that helen would dare to want and even touch somebody else and would be like “what the fuck are you talking about” and hector would either laugh at him or feel sorry for him, depends on what the fight is about. paris would not be amused at all and would want to confront helen but then he walks into his and helen’s bedroom and then she just sits there, wearing a beautiful dress and helen is just like “oh hello, is anything wrong, my dear?” and because paris is paris he forgets everything he wanted to say except “no nothing, i just missed kissing you”.