I was staying at my mates house for a few days and 1 night he was fucking his gf and her moans were so loud and got me hard. I sneaked to the room door and watched. They seen me and told me to join in. He filled her pussy with his cum before I got to fuck her. She told me she wanted to be a little cum slut and have both our cum inside her. Ended up being the best few days ever. The look on the girl face when getting the cock.