I 24F went to a weekend birthday bash with my sister and her close friends. On this weekend getaway I F24 connected pretty well with one of my sister’s F22 friends F22. I think even everyone else at the bash also picked up on it - flirting/connecting going both ways between the two of us. To get to the point my sister’s fiancé M22 pulled me aside and asked me if something was going on between my sister’s friend and I. I told him that I was interested and my sister’s fiancé laughed and said that he knew it and clocked it from the start and thought that we would make a cute couple etc. Besides that comment my sister’s fiancé also made a comment that my sister wasn’t going to like that, and I just kind of questioned why confused and all at that comment. He just said that’s how my sister is and he knew she wouldn’t like that. I don’t know if this is like a family absolutely no-no between sisters or what but this would be the first time something like this has happened. My sister’s fiancé wouldn’t go into details and all he said was that she wouldn’t like that so I am just curious if I am overstepping in some sort of way. Of course I want to be respectful to my sister, but at the same time I am very interested and I feel I connected with her friend, and want to ask her out to coffee sometime. I don’t know if this is a thing where I need to have a conversation with my sister to see if she would mind but also we are all adults so at the same time I find it silly to even have this conversation but maybe I am looking at things in a different way then she might be. Has anyone ever dealt with anything like this and have any input on the matter?