HUNTB-173 - Sharing everything including boyfriends and cocks

When I was dating the younger sister, I ended up getting involved with the older one too. The sister didn't know, so it wasn't a 3P, but since they shared an apartment, I'd enjoy comparing them while the other was showering or out shopping. She'd say, 'I'm going to sleep, do whatever you want!' knowing full well she was watching us. We were both turned on by that unspoken agreement, and we'd sneak around to have sex once she was asleep. We almost got caught a few times, but the relationship was so addictive it lasted for years.