So i came back from college finishing up my freshman year at college. So i head over to my good friends parents house to hang out and meet up with all my friends. I arrive and hb9(in high school still 17) opens the door for me. Me and her have always been with eachother, I always make her laught and shit. She's telling me how attractive i have gotten since college and how much shes missed me. I know shes sending me iois and everything during our conversation. So I end the conversation with her and tell her I gotta meet up with all the my friends in the back. We hug and both make out for a couple seconds and part ways LOL.(

But anyways we have a flirt game goin with eachother, the problem is that shes is 17 and also has a boyfriend who I know she has feelings for...
Its been a month since this shit and i wanna respect my best friends sister and such so im a lil lost in what i should do?

As she is only 17 it is even more dodgy.. its not just your freinds sister but his 17y old sister so your freind is even more likely to get anoyed with you.. as you have made out with her already, this already has the potential to really blow back in your face, its your best friends 17yr old sister.... you might loose your freind it depends on his personality is really... my natural freind & i are always joking about another mates older sister when he is around (she is hot..) and he doesnt care, he will laugh aswell and then take the piss... actually my natural freind even his older siters number and they txt....