My college professor saw my hard cock as I was jerking off to her [MF] | 2016

This happened a few years ago during my junior year of college, I was 21 at the time. It was the end of the semester and I had to go to my professors office to discuss some of my final project. This was a professor that I was always really attracted to. She was a milf about in her late 30s. She was a thin red head with thick thighs and a thick ass. It was late in the day as I walked to her office which was located in a separate building. Being busy with finals and having a roommate that never left the room, I hadn't had a chance to jerk off in a few days. I was about half an hour early to my appointment because I had gotten out of class early. As I passed the building, I glanced into her office window to see if she was in their early. Sure enough, she was in there. She happened to be changing her pants and must've not realized that the curtain wasn't fully down. I watched her bend down to pull up her new pants and saw her thick mature ass checks move apart revealing her black thong stretched over her pink asshole and her pussy lips slightly peaking out around her thong. I felt guilty and tried not to stare as I had only peaked into the window to see if she was in there. Regardless, not having jerked off in a while, I was instantly hard. This small building had a small one person bathroom and i figured, since no one else was in the building and I was early, i needed to jerk off real quick just so I could concentrate during our meeting. I went into the bathroom and locked the door behind me. I slide down my pants and boxers completely to my ankles and went at it. As I was edging to the thought of her thick ass bouncing up and down on me and her mature pussy grinding on my cock, the door quickly spun open. Being so caught up in my fantasies, I was confused about what had happened, I turned with my hard cock still in my hand, to see my professor standing in the doorway with her mouth wide open looking just as confused as me. She yelled "sorry!" and quickly closed the door. But I before she did, I am certain I saw her eyes do a long sweep up and down my cock from my balls to the tip. I pulled up my pants, waited about 20 minutes and then went into her office for our meeting. We didn't discuss the bathroom incident at all. To this day, my biggest fantasy is her seeing my cock and helping me finish off in her office. I frequently jerk off to the mental image of those big white ass cheeks gripping that thong.