This happened about a year ago. My girlfriend had been planning a trip to Spain with her best friend, Julie. Julie is tall and slender with great curves and enormous natural D-cup breasts. She has long dark curly hair, fair skin, and a thin waist with a nicely rounded ass. She would be staying over in our small apartment the night before they left on their trip.
That night, with Julie out on the couch, I could not keep my mind off of her. I had often fantasized about my girlfriend, Kate, and Julie having sex since they always made jokes about it. Part of me hoped that on this trip they might actually fool around a little with each other. So, after Kate was asleep I got up and went to the bathroom. The apartment was pitch black and I could hear Julie's breathing and I knew she was asleep. I was only in my boxer shorts, but from just thinking about Julie's huge, pale, perfectly rounded breasts, I now had a huge erection sticking out of my shorts. I slowly walked into the living room and looked over the back of the couch at Julie's curvy body. That was enough. I dropped to my knees and started to stroke it as fast and yet as quietly as I could. Every time Julie rolled over I got so excited that she would get up to go to the bathroom and catch me rubbing my cock. Soon, I came all over my hand, and I promptly licked half of it off and swallowed it. I then cleaned myself up and got back in bed with Kate.
The next day, I discovered that Julie had decided to leave one of her bags at our apartment for the entire trip. I suppose she just had too much stuff or something. Kate and Julie were high in the sky, now, and would be gone for several weeks, so I could do whatever I wanted. I zipped open Julie's suitcase and found a pair of black lace panties and a black lace bra. It was a 36-D. I brought the panties up to my face and delicately smelled them. Now for the climax to my story.
I went into the bathroom and took off my clothes. I then pulled Julie's underwear up over my ass and my cock, which was now sticking straight up out of the waistband. I love the way women's underwear feels on my cock and the tightness around my ass, and the fact that this was my girlfriend's best friend made it even more arousing. I then put her 36-D cup bra on and looked at myself in the mirror as I stroked myself. I had not peed yet this morning, so I had a full bladder and I knew exactly what I wanted to do with it. I lay down in the bathtub, still in Julie's underwear and bra, and still with an incredibly hard erection, and tried to piss through the panties onto my chest. It was hard at first because the thought made me so horny that my dick was pretty hard wired to cum, not to urinate. But eventually I felt the pressure well up inside of me and I let it burst. I felt the panties get heavier as a dark warm, wet patch spread all over my crotch. Then I pulled my dick out and peed all over my chest and Julie's bra that cradled her perfectly hanging breasts. It felt so warm, and right after it was done, I turned on the shower, rinsed myself off, and jerked my cock till I came right in the crotch of Julie's black, formerly piss-soaked panties. I then tasted a little bit of my cum, as I always do when I masturbate; then I rinsed off Julie's things and tossed them in the laundry.
Telling you this has got me so horny that I think I'll go piss through my girlfrined's underwear right now. Cheers!