Like lots of women my wife had put on weight since the menopause. I have always maintained my own fitness and although in my sixties I am still quite muscular and slim. She is over 10 years younger than me. I have never found overweight women attractive and unfortunately when my wife got fat then I did not find her attractive and our sex life waned. It was my fault not hers, as she still wanted an active sex life but I just didn’t find her attractive. We probably had sex about once every two months and although she tried I just couldn’t maintain an erection. I still got horny but got more enjoyment from wanking and watching porn. After a particularly long period of not having sex I suddenly found her taking an interest in her fitness. She was careful about what she ate, and started running everyday. And in a few months she had lost about two stone and was getting her old figure back. Of course I was becoming interested again but she began to turn me down saying she was tired after her run etc. The tables had turned... I suddenly noticed new lacy underwear in the wash basket and realised that the knickers were well used. Sometimes they were very wet and at other times were hard where they had dried. She started taking her runs very seriously and would sometimes be out for a couple of hours. I decided to see where she went. One day when she left I left it 10 minutes and then drove to the local wooded area where I knew she ran. I could not see her running on the track around the grassy open area so walked into the woods to see if she was running there. After 10 minutes I saw a couple ahead through the trees and quietly crept up to them. It was my wife and a man about my age and they were leaning against a tree and kissing. They continually looked around to see if anybody was approaching and their hands were both inside the others pants. I was shocked but felt myself getting turned on watching her. She suddenly dropped to her knees and started sucking his cock as he held her head. After two minutes she stopped and said something to him and then stood up and leant against the tree. He pulled down her shorts and I noticed that she wasn’t wearing any underwear. He got close behind her and pushed his cock into her. He thrust hard into her for a couple of minutes and I could see her rubbing herself with one hand. He then stopped and gripped her hard and I could hear them both gasp as they came together. He stayed like that for a minute and then they both got dressed, kissed quickly, and then went in opposite directions. He actually ran straight past me but not sure if he saw me. I quickly made my way home and she arrived about 30 minutes later. In the past we’d always been open with each other, but recently we’d not really chatted much. I didn’t know what to say. Do I admit I’d followed her? I decided I’d talk to her about our sex life and admit that I’d been in the wrong and that I wanted her. She was reluctant at first and I told her that I thought she was seeing someone else. She looked a bit shocked but did admit that as I had not been interested in her then she thought that I did not love her so found sex with someone else. He was also a jogger who she met whilst running and he did not have a sex life with his wife so they helped each other out occasionally when they needed it. No love involved, just pure sex. It had nearly always been in the woods except one time he came to ours and they spent the afternoon having sex in our bed. She said she understood if I wanted to split up but she didn’t want to, but did want to continue to see her bloke for sex occasionally. I had the hardest erection I’d had in a long time and asked her if she’d met him that day. She said yes and I asked if she could have sex with me the same as she did with him. She knelt in front of me and started sucking me and then after two minutes she said fuck me from behind. She leant against the kitchen table and I pushed hard into her. It slipped in very easily as she was still full of his spunk. I didn’t last long and she rubbed herself to orgasm as I came in her. We now have sex every time she comes back from running. I have even started to enjoy licking her as soon as she gets in. Something which she actually suggested. She likes to make me lie on the floor and then sit over me so that his spunk runs into my mouth. She is actually quite aggressive as she orders me to lick her clean and always cum hard as she forces herself onto my mouth She spends the occasional afternoon with her new boyfriend and always wants to use me when he’s gone. Happy days.