Sharing Is Definitely Caring

My stepdaughter recently got divorced and as a kind of way of making her feel better, her mother asked me if I'd go round to her home and redecorate her living room, kitchen and hall stairs and landing.
It took nearly three weeks because of my work commitments, and because throughout we were fucking.
Right from day one Lucy was teasing me. She asked me if it was true I'd slept with a lot of women. When I said a few, she replied "My mum said you've slept with over eighty". Before I could reply Lucy added "And mum said it's because you've got a big one".
The next day she mentioned she desperately missed sex and if I wasn't married to her mother, she'd definitely seduce me.
Only a few minutes after she'd said this my wife messaged me this, and I've kept it as proof "Hi, can you make sure Lucy's well and truly looked after. She deserves a man right now".
Her husband had cheated on her, hence the divorce, but it wasn't with another woman.
As soon as I got the message Lucy shouted for me to help her upstairs. I walked up expecting to move something or other, but instead entered her bedroom when she said "I'm in here" to find my stepdaughter totally naked and playing with her pussy.
For the rest of the afternoon we tongued, sucked and fucked one another.
Lucy is twenty nine, slim and has a beautiful pussy and arse. Her breasts are small, but I've always been a leg and arse man, so seeing her naked that day, trust me my cock became rock hard immediately.
We fucked, took a break to have a drink, then fucked again and again.
I'm not sure how many times my stepdaughter orgasmed on my tongue and cock, but she like myself was sexually exhausted by the time I left to drive home.
All my wife said was "Lucy's just messaged. She said you really know how to look after her".
I've since read other messages between them, and I never thought women went into so much detail about what they did during sex, especially with their mother.
Each day I went round to decorate we had sex. Sometimes it was just Lucy sucking on my cock, or me spending time to devour her gorgeous pussy and arsehole. But mostly we fucked like teenagers and I soon learned that my stepdaughter is a real dirty bitch in bed, or anywhere else for that matter.
One evening as I was clearing up out in her back garden, she walked out, knelt on the garden bench and lifted her short skirt.
I fucked Lucy from behind not caring if her neighbours saw us, and apparently one did.
The last weekend I was there, my wife suggested I stay over. I hadn't seen the messages by then, but I was pretty sure my wife Lucy and I were fucking. That's because she said as I left to drive over to her daughters home "Save some for me on Sunday night".
Lucy and I have had sex several times since, and later today she's visiting us. Her mother has asked me not to say or do anything 'nauhty' with Lucy in our home, but she did say "It'd be nice if you and Lucy drove down near the river later".
I know full well what she meant, as my wife and I would often have sex in the car by the river when we were dating. It's a secluded spot and I would spend ages tonguing out Lucy's mum before we fucked.
I know Lucy will eventually find another guy, she's too beautiful not to. But until then I'm going to look after her mothers daughter every chance I get.