Is it ok to get with my best friend's sister?

So I was at my best friend's 21st last night. Her and her partner Dawson have been together for 5 years and I absolutely love them to bits. Were super super close friends. Billie was turning 21 and we did the traditional get wasted and dance thing that everyone seems to do. I've always hung out with girls in my group more than the guys. So when we got to the dancing vs talking, I chose to go dancing with the girls. It was Billie, her sister in law Jayde and myself. My memory is a bit hazy but Jayde and I ended up dancing together. Then it progressed and she started kissing me. I've known her for nearly 8 years now and she's 3 years older than me. I've always kind of been into her but I never bothered for whatever reason. We danced some more and I lead her to the couches where we made out for a bit. I asked her if she wanted to come back to my flat and she replied "no, because Dawson would see us leaving together and he won't be happy about it". Billie knows that we were getting a bit too close and she also said the same thing. She's cool with it as long as Dawsy doesn't find out. We continued go dance the lights came up. We sat outside and this other girl started talking to me. She ended up coming home with me and we had sex a couple of times this morning. I feel bad taking some other girl home in front of Jayde. But I also would have liked to maybe see where things can go between Jayde and I.

So what are your thoughts? Is it ok to get with your best friends sister? Is taking another girl home a massive fuck up? Should I try and get Jayde's number and see if she's interested in seeing me without Billie and Dawsy?
Is it ok to get with my best friend's sister?
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Girls, if you were in Jayde's position, how would you feel? Would you try and contact me or would you want me to contact You?
Is it ok to get with my best friend's sister?
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