Sarah talks you into it

"I just don't know, Sarah. I know you think nothing will happen if it's you he cheats with, but what if it does?" You wrack your brain, trying to collect your thought. If only you hadn't liked what you saw in Robert's cock. If only you hadn't loved the flavor of it enough to blow him, just to see what his cum tasted like. If only you hadn't let him touch your bare pussy like he did. If only you could stop thinking about it, wondering what would have happened if you had allowed him to continue.

"It won't get out of hand, unless you let it get out of hand" Sarah says as she comforts you in her arms. "I'd do nothing to hurt you. Besides, you want Nicole getting her mitts on him? You know she'll try to steal him from you. With me, you won't have to worry about it. If you want me to fuck him, I'll fuck him. If you don't, I won't. You have my word, sis." She kisses you on the cheek. "I love you. I just want to help."

"I have to tell you something else, Sarah." You take a deep breath. "James left because he was upset with me. I made him pull out before he could dump his cum inside me. The reason why I did that was because I kept thinking about Robert's big cock inside me, squirting so much cum in me that it sprayed out of my pussy around his cock. I just suddenly felt like I was betraying him."

Sarah looks shocked and startled by your words. "Oh my. This is bad! But it's nothing that can't be fixed. You just have to stay away from him, and see it for what it is, an infatuation. Otherwise you're going to end up fucking him, and end up pregnant with his baby! Is that what you want?"

"Yes! NO! I don't know!" you answer with a sigh. "I really don't know."

"You are totally fucked up!" Sarah says point blank. "But we can still make this work. Isn't it every man's fantasy to fuck sisters? And I bet James is just like every man when it comes down to it. Let him have sex with me, then you won't feel so guilty about what happens with Robert. I could even move in, and we can all share that big bed of yours. We could both end up pregnant, and no one would ever have to know it's Robert's, if it happens that way. So, will you do this?"

You see no other alternative. "All right. We'll do it. You can move in with us. Say they're painting your apartment, or something, and you need to move in for a while. James will accept that. Then we'll get to work on him together."

Sarah laughs. "We are still devious together when we want to be. You won't regret this."