My new girlfriend's recently left her husband and moved in with me. They had a family dog that was quite old and last week it became very sick and her ex husband called her to ask if she would accompany him to the vet to get it put down. It seemed like a perfectly reasonable request so she agreed to go without hesitation. We had often discussed his infidelities when they were married and she had said she fantasized about being close to him with my cum inside her cunt, and she said the thought of this was a big turnon for her. So immediately before she planned to leave to meet him, we fucked and I came deep inside her, and she rolled back on the bed to tilt up her hips so the semen would ooze back inside her. She then pulled on her panties and jeans and left. I was so looking forward to her returning home so she could tell me about how she felt sitting next to him in his car to and from the vet, and had half a hardon the whole time she was away. When she eventually returned she looked quite flustered and flushed, and it was immediately obvious that something had happened, other than putting the dog down. I could see she wanted to tell me and it didnt take long before it all gushed out:- after leaving the vet, her ex drove directly back to his house and asked her to come inside for a cup of tea. She was happy to join him, enjoying the feeling of my cum squelching around in her panties, and by now it had soaked through her jeans as well. No sooner were they inside and her ex pulled her to him and pushed his hand down the front of her jeans, telling her he could smell cum on her, and telling her how much it had turned him on the whole time in the car on the drive back home. She said she initially resisted and pushed him away but he pulled down her jeans and buried his nose and face in her pussy. Pushing her back onto the couch he pushed her legs apart and began licking and tonguing her deeply, tasting my cum. She said her orgasm was virtually instantanous, shuddering and bucking with his tongue inside her. He then pulled out his erect cock and fucked her hard and fast until he came inside her, triggering another huge orgasm for her. This was a real surprise to me because she has always been a woman who needed time to reach orgasm, and considerable time of deep penetrating thrusting and clitoral stimulation before climaxing. She told me that they both then pulled apart and the shock on her face must've prompted her ex to explain that he had always fantasised about tasting another man's cum inside her, throughout their marriage, but that he had never imagined she would've been prepared to let another man fuck her while with him. She said she felt confused and couldn't really process what had happened and how much she had enjoyed it and also what he had just said to her so she pulled on her pants and jeans and left in her car in a hurry. But this story had by now completely turned me on, and my stomach was churning with lust for her. My pulse was racing. The thought of her sitting next to me telling me she had just been fucked and still had his semen inside her cunt had aroused me to the point of premature ejaculation.... my cock head was slimy with precum oozing out the engorged and swollen head. I pulled down my shorts and it sprang out. Pushing her head down and pushing as much of my cock as possible into her mouth, i slid my hand down her jeans and felt the wet slimy pubic hairs and labia, soaked in her ex's cum. I could not resist, and pulled her clothes off and spread her legs up in the air, burying my mouth and face in her cunt. Without touching my cock, it erupted within seconds, spurting cum all over her and the floor. I didnt realise what a cuckold was until that moment. And I am still trying to understand how to behave from now on, with my girlfriend, but one thing for sure is that I am looking forward to more of the same, hopefully.