Mixing My Roles

My best friend at work invited me to his mothers new home (His mum and dad are divorced) about two months ago.
When we met we both immediately recognised each other, but didn't let on we knew one another.
And the reason why is the last time I met Tia, she and another woman from a party i attended, had sex at Tia's old marital house.
I'm a twenty one year old out of the closet bisexual guy, one who's been sexually active with both sexes since I was fifteen. At the age of eighteen I spent two glorious hours fucking two older women in a house, one being my friends mum who Very much enjoyed my large cock that night. Her husband and son spending two nights away fishing.
Tia and I went on to fuck several more times, mostly in her car at a well known car park for lovers.
We stopped mainly because I began having sex with a guy my age, who didn't like I was fucking a married woman.
What I haven't told you, is the reason my friend invited me to meet his mum, is I'd been fucking him for a couple of months and he'd told his mother we were coming for Sunday lunch.
It was a little awkward at first, but Tia kept silent and so did I. When her son went to use the toilet, we quickly spoke about our past liaisons and about me being with her son.
The one thing Tia did ask, was "Is your cock just as big these days".
I couldn't resist flopping it out in front of her face as she sat on her couch and hearing her say "God that's bigger than I remember".
Before I left Tia made an excuse to take my number, just in case she couldn't get hold of her son. But we both knew the real reason.
Three weeks ago with her son on a different shift to me, I spent the whole afternoon fucking Tia in her home.
She was just as dirty as I recalled and if anything wanted anal sex far more than before.
What's crazy, is I met her son after he finished his late shift and we fucked in my car at the back of the airport. What's more as I fucked him bareback, I thought to myself 'I haven't showered since I fucked his mum'.