Shannon knew I still had feelings for my Erin. We were living in my father's basement, saving up for an apartment. One night, in the middle of sex, she told me to stop right as I was getting close to orgasm. She said she wanted to do it someplace new. We got dressed and went for a walk, down the street to my Erin's house.
Very quietly, she hiked up her skirt and leaned against the siding underneath my ex-girlfriend's bedroom window, facing the street. It was 3:00 in the morning, so I wasn't as worried about cars as I was my ex-girlfriend waking up. Her bed, I knew, was a few feet from the window, on the opposite wall. The siding creaked with our movements as I fucked her standing against the wall, just a few feet away from where she slept.
Perhaps it was poetic justice that when Erin and I got back together, we fucked in our apartment... on our couch, in our bed, and on our kitchen table, with her naked ass right at the spot where Shannon ate. I ended up leaving Shannon for her. She was right... I still had feelings. Less than a year later, we were married.