Well, my sister has been going out with her boyfriend for 1 year now and every time they come over by the house me and him always start talking and we sometimes flirt in some weird way. Then my sister gets pissed off at me because I talk to him and I'm being "too nice.." He's sorta like my best guy friend. I know and he knows that he loves my sister but it's this feeling every time I see him that there's something that could've happened but I really doubt it. I don't even know if I like like like him.
Yes, I would definitely stop flirting with him. It's okay if you guys are friends, but you don't want to break up something that him and your sister have for a little crush, do you? I honestly don't think it would be worth it.
Yes, you have to stop flirting on him. There's a lot of guys out there. Don't be selfish. Think about what your sister's feelings and if you are in her shoes. Are gonna be happy is your sister gonna steal your bf? Think about that.