Read 1/2 first.

"Was that story true Emma, have you actually fucked Mark?" I said trying to get my breath back from the most intense orgasm. She turned to Me trying to judge my facial expression. There was a long pause before she spoke. "Well do you want it to be true? Do you want him to fuck me?"

I was torn, confused, jealous but I was very horny. I still didn't know if it actually happend. Was I going to be setting my self up by answering yes, Allowing her to take our game to the next level. Was she just seeing what I thought? Never to progress further but just testing me. I had left her waiting for to long as I decided my fate.

"Yes I think it was so hot, I wish I was in the next room listening to him fuck you, use your body in ways I can't" as I said this I reached down and started to rub her clit. She moaned and bit her lip. "Good boy Jack, Mark is going to be happy" she placed a hand on my head and pushed me under the covers. I pushed my tongue deep inside her pleasing her, as if I was rewarding her. I forgot I had cum inside her minutes before,as she was telling me the  story. That didn't matter right now I knew what I had to do. I paused for a second and asked her to tell me more.

She began her story again with more detail of how they hadn't just kissed in the club, how he'd managed to sneak a finger past her thong and slide it between her pussy lips, feeling how wet she was. She told me how she climbed on top of him in his room and lowered her self on his cock. His hands on her tits as she bounced up and down on him. How he had kissed her deep while he was buried inside her. She explained that there was no thought of the consequences by either of them he knew what he wanted. Every new detail I would try to put my tongue deeper and pleasure her more. I wanted to know more, I was hooked. We carried on most of the night story telling and playing with each other.

The next day I woke up before Emma. I looked at her fast asleep I loved her so much. The pain of jealousy hit me. How could she do this to me, how could they both do this to me. The rest of the day I was off with Emma I was hurting so bad letting the anger and jealousy build up inside me. I didn't like the image of them two fucking anymore. She was meant to be me girlfriend my future wife. She had really crossed the line and cheated on me. She noticed in the afternoon that something was the matter. So when we sat down for dinner she confronted me.

I told her how hurt I was and that she shouldn't of took or fantasy game to the next level without my Consent. How I loved her and felt betrayed by both her and my so called best friend. As I was blabbering on she she stopped me and shouted "Are you for real, I haven't fucked Mark this was just part of the fantasy game. Not once did I say it was true"!! I was so confused, I started to stutter but she cut me off again. "I'm upset you'd  think I do it behind your back. You told me last night you wanted the story to be true.  You wanted me to fuck Mark". She had me, I'd confessed last night I wanted it to be true. I even stated that i wished I was there listening. I started my apologies and pleas I told her how stupid I had been and that I loved her so much It just felt so real it had made me realise how much she ment to me. She didn't come round straight away. She went out that day for a few hours, leaving me to stew over what had happened. Stupidly I masturbated to the thought of them again. What was happening to me why did I keep finding the thought of them such a turn on. 

Our life changed from that day we were still in love and lived happily together. We stopped playing our fantasy game. Our sex life wasn't what it used to be. We still fucked but not as dirty or as much as we use to. I still thought about Mark fucking Emma it was the centre of my now bad porn habit. Cuckold porn, girlfriends cheating anything that was to do with partners fucking others I was into.

We stopped going out as much, We started saving money to finally get our first house and move out of our apartment. I started working most weekends doing as much overtime as could. One Saturday when overtime was called off.I was at home chilling out with Emma, it had been awhile since I'd done anything nice with her. I decided to run her a bath and cook us a nice meal. While Emma was in the bath, I was in the kitchen cooking. Her phone buzzed on the side. I don't know why but I decided to have a peep at who it was.  The contact said Amy, I opened the message. My heart skipped a beat as I read the message.

How's my slut? Are we still OK for today? I can't wait to feel your pussy on my cock. I'm going to give you what you need today.
I stood there froze reading the message I scrolled up there were lots of texts back an fouth. The message were extremely dirty but there were also messages saying he's gone and it's safe. There were pictures messages also. The pictures were of Emma she was naked on our bed some really naughty photos, legs spread, tits out with fingers in mouth. There were also pictures of someone's cock, it was much bigger than mine it was atlesst 8inchs. It had been sent to her alot of times, sometimes with a hand around it. I checked the contact details of Amy. I put the number in my phone. You guessed it, the messages were from Mark.

I put her phone down and stood in a daze. My cock was so hard. I was trying to think what to do with this information. What do I say to Emma. I decided I needed to see this with my own eyes. I was in denial, maybe they were just dirty texts like our fantasy game. I ran to the bath room door, I told Emma work had called and they wanted me to go in. I told her I won't be back till 9 tonight. I jumped in my car and parked up round the corner. I waited 2 hours until I saw Marks car pull into my estate at the apartments. I waited 5 minutes and ran to my door. I had practiced creeping into to my apartment many times due to coming home pissed at stupid old o'clock In the morning. As I entered the apartment the sounds were obvious. It was the sound that I'd heard many of times in the spare room at Marks. This time though it wasn't some random girl. This was my Emma being fucked. I notices Marks boots my the front door, as I made my way down the hall. Luckily the bedroom door was slightly open so I could see into the room through the crack of the door. I wasn't disappointed at was I saw. Emma was holding onto our head board, Mark had both hands on her arse checks, pulling then apart. He was fucking her really hard. I could see Emma clinging onto the head board to stedy her self. Her head was up looking at the wall her eyes shut tight.  She looked like she was lost in the moment. My cock was about to exploded, I wasn't jealous I was turned on. How had she kept this from me for so long. I decided to leave and return to my car. I masturbated in right there in my car. I didn't even take my cock out I rubbed it through my trousers until I cum. There I was sitting in my car cum all in my pants. While the love of my life was being nailed by my best friend in my own bed. I waiting for another hour until I saw Mark leave.

Tbc. honestly thanks for the comments.
This is truthfully what happened I have changed some parts for your pleasure but most of this tale is true.