For the first part of the story you can go here: https://www.reddit.com/r/gonewildstories/comments/56csan/how_i_then_18m_started_fucking_my_then_18f_cousin/
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When I got back home after that cabin trip things with my girlfriend went back to normal. Secretly Lisa would send me dirty pictures or she would fuck herself with her hairbrush while I jerked off over Skype. Eventually it died down because her boyfriend, Josh, was accusing her of cheating even 5 seconds. We weren’t in love this was purely lust. As far as we were concerned it was like masturbation so we could live without it.
About half a year later Lisa got accepted to university close to my house and it worked out that my sister had moved in with her boyfriend Lisa came to stay with us to save of tuition costs.
By this time I was head over heels for my girlfriend so Lisa was just a memory which worked out great for about a month. Lisa and Josh broke up while she was on my side of the country and she soon became lonely. At first I didn’t really notice because she never overtly came on to me. But slowly I noticed she started teasing me with her body. For instance I would walk into the living room and she’d be sitting on the couch in short shorts and spread her legs gently to reveal she wasn’t wearing panties. Or bend over in a short skirt. Running from the shower to her bedroom in a towel but letting it slip a little as she got by my room.