I had spent a long time trying to persuade my ex girlfriend to get into swinging and although she was sexually adventurous with me she used to switch off at the idea of swinging. I gradually came to realise that this was mostly to do with her jealousy over me and not wanting me to sleep with other girls. This was because she used to get really hot whenever i would talk to her about having a threesome with another guy and her biggest fantasy turned out to be being taken by a group of 3-4 guys all pleasuring her in every hole. I pushed at the idea of a threesome and she agreed on the condition that it was with another guy and not a girl. We spent a while browsing together looking for a suitable guy. She wanted someone around our age at the time (18) who had a nice body and would meet near to where we lived. Eventually she settled for a guy named George who was a few years older than us who said we could have a threesome in his van or at his work. Little did i realise that while chatting to him he had persuaded her to have a mff threesome with him with her friend Susanna. So I had effectively organised my girlfriend to have a threesome with another guy and been cut out of the end result. What added insult to injury was the fact that this guy was going to get to experience what was my fantasy of having two girls please him and one of them was my girlfriend! I finished college and went over her house and Susanna was over. They were chatting to George online and i asked what was going on. Amy smiled and told me that the threesome was organised her hand playfully squeezed at my crotch and she kissed me. "The only thing is he didn't want to share me with another guy so Susanna is coming with me." I didn't know what to say. I was angry but at the same time I felt like she was only doing it because i had told her to. I was turned on at the idea of her being fucked but i had wanted to take part in it. Also i was really jealous of this guy because Susanna was hot and it upset me that Amy would have sex with this guy and her but not me and her. As all this was spinning through my mind they were putting makeup on and tossing things out of her wardrobe. "Where you off to? To see him?" i asked half joking. "Yeah we're meeting him in an hour." My head was now spinning, before i knew it she kissed me and left down the street with her friend both looking like Escorts. I decided that i wasn't happy with the situation and i at least wanted to join in. I called Amy to see where they were so i could meet them. In the background i could hear Susanna moaning as she was being fucked. I was instantly turned on and curious as to whether Amy had done anything. She wouldn't let me know where they were (I later found out she enjoyed the power trip of denying me and controlling these sexual encounters) but also said she didn't find him attractive face to face and so wasn't doing anything. I picked them up Susanna looking a little happy with herself and flushed (I later found out she was a virgin before that experience) and took them back. Amy after that turned off the whole extra-relationship activities again. She used to tease me sometimes that she had sucked George's cock with Susanna to wind me up but i believe that nothing in the end happened that night. I ended up going back to uni so was away for a few weeks before i saw her again on the weekend. We had a nice night in watched a few films and ended it off with some amazing sex with me cumming inside her. As we were drifting off to sleep her phone began to vibrate. She answered it and after a brief conversation filled me in with the details. Basically her friend Sam had been out drinking for the night but had been ditched and needed somewhere to stay. As we were in her mum's house Amy would have to stay downstairs with Sam. She asked if i'd be ok with this and then to which i said it was fine. She then told me that Sam was a guy and teased me that she found him quite attractive. I teased her back and said well you can only let him lick you as he'll be licking my cum. After the week before i doubted anything would happen. She came up in the morning and got back into bed with me. I started to rub her clit ( I'm always horny in the morning) initially she told me she was tired but i persisted and eventually she turned round and kissed me "You'll never learn will you?" I started to suck her nipples and she gently pushed my head down until i was licking her clit. She was really wet as she grinded her pussy against my face and bucked her hips. Holding my head in place after a short while she came in my mouth and told me to swallow every last drop. Her legs shuddered and she pulled my head up and away as she began to relax. As i came up she smiled and said "It's your mistake..." a look of mischief and satisfaction in her eyes. I began to realise what had happened as i went to have sex with her and she pushed me to the side. "I've been fucked this morning already" she then laughed to herself "it was you that ended up being the cum eater". She then proceeded to tell me that when she went downstairs she was initially going to go to sleep but her hand ended up on his cock which she then had to suck and then had to let him fuck her till he came, which he did multiple times throughout the night. She hadn't told him he was fucking her while her boyfriend was just upstairs. I later found out that he had been regularly fucking her while i was at uni but she didn't want me to know so i would remain faithful to her. She was slowly beginning the process of cuckolding me......