18 year old house guest

My GF was working with a young 18 year old girl, that wanted to move from her parents home. We had an extra room, so we decided to rent it to her for as long as she wanted. Really cute girl, with a perfect body, quiet and polite and very pleasant. I had to do some work in her bathroom, she just got out of the shower and was putting on her make up. She said go ahead, and while working right next to her, I was laying on her dirty clothes pile. She left as I was finishing up so I was in the house all alone, and I counted 8 pair of her panties in the pile. I grabbed the pair on top, and they were warm and wet. I knew she took them off before showering. I couldn't resist, so I picked them up and started smelling them ! It was incredible, to have the scent of a young and different girl. My cock got so hard, I had to let it out. I could not stop sniffing her panties for about 30 minutes. After a lot of pre-cum, I used it to rub the head of my cock. It only took a couple rubs before I exploded all over her bathroom ! Ever since, I've had a desire to find used panties...