My girlfriend and her friend Erin came back to our apartment drunk as a skunk after "girls night out". My girlfriend went to bed and sent Erin into the spare room. It was almost 3 am and Erin seemed to be in the bathroom along time as I was sitting in the living room watching tv . She went into the bedroom leaving the bathroom and hall light on, I just sat there for about 15 minutes and decided to go to bed myself. I went to turn the lights out and Erin never closed her door all the way and was laying naked in the bed on top of the quilt. I stood there looking at her for at least 20 minutes with a hard on and walked right up to the foot of the bed. I have great sex with my girlfriend but just the sight of Erin made me jerk off. She has a perfect body and a shaven pussy with perfect size breasts. I finally turned the lights out and went to bed. I mistakenly told my girlfriend I saw Erin naked not saying I jerked off. I have a big mouth because my girlfriend told Erin I saw her and there is another girls night out next month . I did lie however saying I only saw her for a second or so.