An older man gets inside girlfriend's knicker SeXStoRY

I suppose that ever since I spyed on my supposedly straight-laced, church-going s****r and saw her lovingly licking her boyfriend's erect cock to orgasm, I have been fascinated by the differences in the outward appearance of people and what really goes on behind their closed doors. It's very difficult to take a lecture on sexual morality from an older s****r or anybody else who you've seen dressed up as a sexy nurse with cum trickling down their nose. So now I always imagine the miserable looking, bored and buttoned-up receptionist at the office perhaps going home to be tied to the bedpost and fucked liked crazy by her husband, or the very correct secretary pulling her knickers down and sitting on her boyfriend's face as soon as she gets home hot and sweaty. Mike and Anna, two of our best friends, are also very unremarkable people at first glance - or at least I used to think so. Mike works as a sales manager in the industrial gas industry, and his wife works as a sales assistant at a department store in town. The only remarkable thing about them being their age gap: he being about 48 or 49, and she being 23. They've been married about twelve months now but are still very much in love - always sitting close, touching each others legs and intertwining toes whenever we're round at their flat. Eager, I guess, to fuck like mad as soon as we've left. Now they've recently moved into their first house together. A very ordinary semi in a very ordinary looking street on a new estate. Anna and my gf are very close friends, having shared a room together at college. My gf says they even used to menstruate at the same time - true s****rs. But with Anna being the more adventurous and promiscuous one in bed - or that's what the gf always used to tell me. My gf has told me that Anna had lots of men and cock of every shape and size before she met her soul-mate Mike. She tells me she's seen Anna in almost every sexual position known to man, the girlfriend having had a ringside seat whenever Anna used to bring her men back to the college dorm. Anna and the gf seem to share almost every sexual secret - like most ladies do. I hear about everything Anna and Mike get up to, and it always gets me turned on to hear about the sex toys they use on each other, so I'm sure they also know about what two we like doing: dressing up and role play. So given that Anna is always very flirty with me when I'm round at her house, it came as no surprise when the gf told me that Anna had suggested that me and the gf swap partners and see how we all like it. Given that I had long fantasised about what Anna looked like undressed - her tits looking gorgeous whenever I used to get a chance to look down her blouse as she served coffee or up towards her fantastic full fleshy inner thighs as I peered up her skirt as she sat opposite me on the sofa, I was immediately aroused by the prospect of fucking her for real. I've been unable to think about anything else for the last week, but to my surprise, I was also strangely excited by the thought of watching the gf being fucked by an older man. Things haven't been going too well between us sexually - so I thought this was the chance to break down last the sexual barriers between us. There are so many things I want from her sexy body that we haven't yet shared, this was my chance to liberate us, I thought. So when we went on our first date as a couple yesterday afternoon, feeling more excited than on a first date with a girl you've always wanted to fuck, I could feel my cock swelling and then rising in my boxers as soon as we arrived outside Number 27. As soon as I was in their small hallway and saw she was dressed in high heels, a tiny pleated blue skirt, black stockings and white buttoned blouse, I knew Anna and the gf had been doing their research and swapping notes on me. Mike was coming down the stairs at that moment, looking very athletic in tight rowing shorts which showed his balls and lengthy cock in outline, with a towel around his shoulders. Again, I guess, the result of the gf and Anna sharing their s****rly secrets. But it was not until after a few drinks and some "dancing" - grinding my hungry cock against Anna's waiting vulva, and we went upstairs to bed that all the secrets were to be revealed....