There had always been an attraction between me and my sister-in-law. Even when I’d been living with her sister – and then even engaged – that tension was always there between us. I used to look forward to the days during the summer when my sister-in-law was single and would call over sometimes for a barbeque. In a summer dress, with bronzed legs and cleavage showing, I’d often have to remain cooking at the barbeque longer than I’d planned just so I could hide the raging hard-on in my shorts. Whenever I’d have a few minutes free, I’d have to sneak off to the bathroom to stroke my cock until I erupted a stream of hot cum as I fantasized about my tongue exploring her ass and wet pussy while we did a 69. I remember one barbeque where I returned from the bathroom after having to wank my cock until I exploded after getting a flash of her thong under her short dress. From the corner of the patio, I could see her smirking when I resumed cooking duty. She walked over a couple of minutes later, her dirty blond hair curling over her bare shoulders. She handed me a fresh bottle of cold beer and leaned in to look at the sizzling food. “Do you need a hand?” she asked, giving me a sideways glance with one eyebrow raised and her mouth curling into a suggestive smile. I looked purposely straight down her cleavage as she looked at me. “I think I’m ok now,” I grinned back at her. I could smell her perfume and see her hard nipples pressing against her cotton dress as her green eyes pierced me. “Well,” she said, lifting her own beer bottle to her mouth and then subtly running her glistening tongue over the top, “don’t be afraid to ask if you need some help. I’m good with my hands.” She turned before I could answer and left me with another hard-on. But long weeks would often pass before we’d see each other again. My wife – her sister – and I got on fine, but there was always something about that forbidden fruit that just got me so aroused, especially when I knew the feeling was mutual. The flirting and suggestive comments would continue, and my wife and everyone else was oblivious to it. It was our thing. The first time we got really close to anything happening was one time at her place. There were a few of us there, but people were drifting in and out and at one point everyone left for an hour or so. I went for a run and came back to the house, ready to take a shower. I was hunting for a fresh towel upstairs, when suddenly she emerged from the bathroom, a towel wrapped around her, fresh out of the shower. I jumped when she said hello, not realising she was still in the house. “Sorry, I didn’t mean to startle you,” she said, when clearly she had meant to do exactly that. She looked me up and down, my arms and face still glistening with sweat. “I’m looking for a towel,” I said, stepping so close to her that we were practically touching. I looked at her towel and had a vision of pulling it off her. She read my mind and grinned, looking me up and down. “Mmm, you’re all sweaty.” She rubbed my arm. And then, all of a sudden, she just took off her towel and handed to me. My mouth dropped open. Her shaved pussy and erect nipples were just inches from me. She raised her eyebrows and put her hands on her hips, leaning them to one side. “Well, you’d better hurry up and have that shower. Or, maybe there’s something else you’d like to do.” She turned, looked over her shoulder, and walked to her bedroom, her ass swaying as she walked. I couldn’t take it anymore. I began to follow her, feeling my swollen cock in my shorts, bursting to get out. I wanted to lick every bit of her, feel her riding my face and then to push my cock deep inside her pussy and ass. And then there was a click. The front door opened. In walked my wife and two of her friends. I waved hello from the top of the stairs and said I’d be down in a few minutes after my shower. My sister-in-law stood for just a couple of seconds at her bedroom door, faking a sad face and then licking her finger before slipping it into her pussy. Then she winked at me and closed the door. I jerked off in the shower like the world’s survival depended on it. Over dinner that evening, we were all chatting outside as the sun set on another hot day. Talk turned to exercise, and my sister-in-law lamented that she’d stopped running a year earlier because of a minor injury. “I’d love to get back into it,” she said, eyeing me. And before I could say anything, my wife had volunteered me to take my sister-in-law out running with me to help her get back into it. I shook my head and smiled. “You won’t be able to keep up,” I said, teasingly. “Oh, I will, believe me,” she said. And when no-one was looking, she sucked her finger and gave me a wink. Two weeks later, the phone rang at home. My wife answered, chatting while looking at me. She hung up. “That was my sister. She wants you to take her running this evening. I’m going out for a while, but do it for her, will you? You promised. I told her to come about six.” She arrived dead on time, just as my wife was heading out the door. In her tight running shorts and top, my sister-in-law looked incredibly hot. Her blond hair was tied back in a ponytail. “Ok, so where are we going?” I told her we’d take it easy at first, a slow warm-up jog down to the end of the street and for another few hundred yards to see how she was doing. She and I stretched first and I could barely stop myself from squeezing her ass as she got ready. We started off easy, a gentle pace down the road. She looked at me, smiling. “I hope you don’t mind me coming out with you,” she said. Then I noticed her glance down at my shorts, where already it was impossible to hide the swelling hard-on. She laughed. “I guess you don’t.” She ran ahead a little, making me run a bit faster to keep up, both of us starting to work up a sweat already. “I thought you hadn’t run in a while?” I looked her up and down, those smooth bronzed legs working the road. “Well, maybe it just comes back easy.” We ran for about 20 minutes and then turned to head back to the house. Just as we were in sight of it, she pulled up her leg and stopped, holding on to a bench at the side of the pavement. “Alright?” I asked as she stretched her leg and then sat down on the bench. “Rub it for me, will you?” She offered me her leg. I hesitated for a moment, then knelt down, taking it into my lap and started working my hands over her calf. “Up a bit further,” she said, taking my hands and drawing them up to her thigh. “Just there,” she smiled, her tongue flicking across her lips. I let my hands move over her thigh, squeezing it before moving higher and letting the tips of my fingers move over the mound where her pussy was hidden under her running shorts. She closed her eyes as my hands moved, and I could feel my cock getting rock hard. After a moment, she gently pushed me back. “Ok, let’s head back.” Both lathered in sweat, we started walking up the stairs when we got in. She stopped half-way up and she pushed me against the wall, standing in front of me with her ass to my shorts. She pushed her ass against my cock, squirming. “Mmm I just wanted to check how hard you really got,” she said. I pulled her closer, squeezing her tits through her up. I pulled down my shorts, pushing my hard cock against her ass. “About as hard as I’ve ever been,” I replied. She reached behind her, taking my cock in her hand and started stroking it. She kneeled in front of me on the stairs and ran her tongue over my shaft before plunging my cock into her mouth. After a minute, she stood and kissed me, our tongues mingling as she kept stroking me. We moved to her bedroom, and I kneeled in front of her this time, pulling her shorts off her, my tongue finding her pussy. It was soaking wet. I pulled her by her ass towards me so I could push deeper inside her, fucking her with my tongue before licking her clit. I turned her around and bent her over the edge of the bed, kissing her ass before moving my tongue between it to explore her. She whimpered on the bed as I spread her ass, my tongue flicking between it as I fingered her pussy. I stood, rubbing my hard cock over her ass before she turned, and took me deep into her mouth in long, slow motions. My shaved balls brushed her face as she took me right in. She took me from her mouth, licking my shaft and sucking my balls as she kneaded my ass. She pushed me onto the bed, spreading my legs and moving her tongue all over my cock and balls. I lay back in ecstasy, feeling her lick me and then as she spread my legs more so she could lick my ass. I was ready to explode. She stood before straddling my cock and easing it into her pussy, pushing it deep inside her. She squeezed her tits as she rode me, feeling my balls against her ass. “I want to cum when we 69,” she said. I nodded and she slid off my cock. It was covered in her juice. She sat down on my chest before moving up towards my face, her pussy rubbing against me. I put my hands on her hips and pulled her down on me so I could move my tongue al over her pussy and ass. She groaned before I felt her take me into her mouth again in deep, long strokes, one of her hands holding the base of my shaft. Her pussy juice dripped onto my face as I tongued her, teasing her clit and ass. She squirmed on top of me, getting ready to cum hard. I felt myself ready to explode and couldn’t hold it in any longer. Neither could she. She rocked her pussy and ass over my face as my cum gushed into her mouth. I felt it spray in her as she soaked my face. She turned on me, coming up to face me and opened her mouth, cum still inside it. I pulled her towards me and kissed her, my cum in both our mouths as she lay on top of me. We lay there, unmoving, for about five minutes. She looked up at me, smiling. “Want to be my running partner?” I nodded. “I think we should start training for a marathon.”