She's my husband's wife and she's offering me her pussy, fuck, what do I do?

You guys aren't going to believe this, but my best friend's wife offered me her tits and pussy, and honestly, I don't know what to do, haha. On one hand, I'd fuck her without a second thought, but on the other hand, I think you can't do that to a friend. But damn, look at that ass, those tits, how could I not want to fuck either of those holes?