Do I, Or Don't I

My nineteen year old stepdaughter has been teasing the hell put of me, ever since she walked in on her mom and me fucking.
This was six months ago and in a rare opportunity to have sex with my wife at home alone, I was really hammering her asshole from behind when Kelsey walked in.
I saw the look she had on her face as I withdrew from her moms ass, and it wasn't one of shock, but of pure lust.

And since then Kelsey has been flashing me her breasts, her pussy and ass, and even slowly masturbating in front of me, even if her mom is at home.
The other day she walked into the bathroom as I was showering and gripped my cock. She told me it's about time I fucked her.

Now Kelsey is a beautiful young woman and I'd definitely fuck her in a heart beat. However something happened straight after Kelsey had held my cock and stroked it.
We both heard her mom, so Kelsey went to her room. Her mom joined me in the shower seeing my erection with a curious smile on her face, and we fucked. But after we fucked and were drying ourselves, my wife said this "You're obviously now aware Kelsey likes you, you know, that way. I think she needs to experience sex from someone like you, but I don't think I could handle you and her together. Well I don't think I could anyway".
As she left the bathroom, my wife added "I'm playing golf all day next Sunday, maybe you and Kelsey should enjoy the day together, and work things out between you".
I didn't reply other than to say "ok".

But now I'm thinking my wife is giving me the green light to fuck her daughter. And Kelsey has gone into overdrive talking to me when her moms not around, about wanting a real man to introduce her to anal sex.
My only worry, if I'm not reading this right, is my wife using Kelsey to see if I'm a faithful husband. Or do they both want to share me sexually. It's so confusing as they haven't said anything outright.