Should I go ahead and bang my close friends sister?

I have a really good friend who I know from childhood, let’s say, at least 18 years. I know his sister for at least as long too. She is my friend too, but, we’ve recently started having a thing for each other and we’d keep doing innuendos on and off whenever we meet and, every chance we get online, we’ve sexted a bit. I’ve had it with holding things back on both of our ends, but I’m considering about the equation which might get ruined. I do want to ravage her, but she’s a close friends sister. What would you guys suggest? I’ve really tried holding back up until now, but I feel like fucking her brains out at times.