When I was nineteen I set my step mom up with my then boyfriend to split her and my dad up. I knew he just was a cock on legs and would fuck anyone he could get his big dick into. So asking him to call round, I told my step mom I needed to go and get my dad some stuff for when he got home. Saying I'd only be a couple of hours. Parking my car a couple of blocks away I walked back and waited for my boyfriend to arrive. Sure enough he pulled up and my step mom let him in. I waited another twenty minutes and then crept round the back way. My boyfriend was true to form as I guessed he would be. When I walked up to the rear patio doors, I could easilly see him fucking my step mom from behind, as she leant on the breakfast bar. The real strange thing was, watching my step mom take my boyfriends cock up her pussy, was so fucking horny, I actually started to play with myself. I just couldn't hold myself after a few minutes of watching them have sex and opening the door I stepped inside. When all the shouting had finished, I told them to carry on and even guided my boyfriends cock back into my step moms pussy. We spent the rest of the morning having sex, my boyfriend fucking us both. It was only a one off with my boyfriend, as he thought I might tell my dad. It wasn't a one off with my step mom as for the next few months until I moved out, we had sex together. I'm now in a lesbian relationship, but I don't exclussively keep myself to one sex. I haven't had sex with my step mom since that time and my dad has never found out, but as the saying goes.... Never say never!