My wife would go mad if she knew I was writing this. She is a lovely sexy woman and has a fantastic appetite for sex. We have always been adventurous in the bedroom and out in the open sometimes too. We have fantasised about swinging, well not swinging as such more sharing our bed with another guy, but its never happened for real. Karen is not my first wife, I am 50 and she is 39. She has been a great step mother to my Son since we met for 14 years ago. My Son is now 24. We thought things were different when we were young compared to our parents, but boy things are different today. My wife still tidies my Sons room at my disgust, cooks, does all his washing and ironing etc but the thing is, he has no concerns about leaving his personal items lying around even though he knows she is going to be picking them up. We not just talking pants and stiff hankies etc, were talking hard core porn videos, mags, sex toys (for use on his girlfriends I presume) and even his condoms, I am talking used ones, unwrapped just dropped in the top in the waste bin. We have always been and open family. Not always bothering to cover up. Up till a few years ago Karen thought nothing of walking from bathroom to bedroom naked. The bathroom door never gets locked. I have never thought anything of it. Well the other day my son was out, I was cutting the grass and my wife was doing housework. I wanted a drink; I left the mower running as it’s a pain to start again and went in for a drink. I went to ask Karen if she wanted one, I couldn’t find her at first, she obviously thought I was still with the mower because as I looked into my Sons room I found her lying on her back on his bed. Her legs were spread, her dressing gown was wide open at her sides and one of my Sons vibrators was going full speed ahead inside her hairy minge. This surprised me because our room is only next door, and she has several great vibrators of her own so I could not understand why, if she wanted sex she wouldn’t just go to our room and wank. Seeing her in a different environment was so erotic though, she didn’t look like my wife even. She must have been there some time already as I could tell she was near to climaxing and the reason she was there became clear seconds later. She had her eyes shut and was obviously in a fantasy mode, dreaming of something very erotic. She was tweaking her nipples with one hand and thrusting this large vibrator in and out her soaking cunt. As she started to orgasm she arched her back, pulled and held the vibrator hard into her and clamped her legs up and together, and quietly moaned “oh Phillip, oh Phillip” time after time she whispered “oh Phillip” until her orgasm subsided. Phillip being my Sons name. I was gob-smacked, frozen to the spot, and then she saw me. She has always fucked me with her eyes closed while she fantasises, something that I have really enjoyed because I always know that she was imagining she was fucking some other guy. But now I know its my son she may have been dreaming of I don’t know quite how to take it. We fucked last night for the first time since I caught her, but she had her eyes open and looked at me all the time. She just lay there as if she was doing it just for my pleasure and it took us ages to cum, which is unusual, and I know she did not enjoy it so much. Worse still I get that horrid feeling the reason she has never complained about picking up and disposing of his used condoms, never been shy about letting him see her naked may be there is more between them than she dare let on to me.