I was staying in Florida last week and my wife and I shared a large vacation condo with another couple and their 21 year old niece. We were all out at the pool except for the niece. I went back to the condo to take a nap and the I walked in and I heard something in the bathroom. the bathroom door was open so I peeked inside and she was in the shower getting off on the shower massager. This girl was super hot so I stood amazed and instantly got a boner. I reached my hand into my shorts and rubbed my dick and she ended up seeing me. She just smiled and kept going. I realized I was going to cum so I left the bathroom and went to my bedroom. She obviously was disappointed that I left so she tried to tease me by being very vocal in her pleasure. I could hear her in my bedroom and I stood there and soon came all over the floor. My wife and I have had threesomes but I really wanted to go in the shower with the niece and fuck her like crazy. Would it have been okay to do her or did I do the right thing?