Fucking My Wifes Friend

We just had a barbecue the other day and my wife invited a few friends over and one of her friends was wearing a sundress and she was sitting on the couch and I was standing in between the door way and the kitchen and my wife was outside by the pool and when her friend got up to go t the kitchen to get another beer her sundress has gotten stuck to her skin on her back and I saw her ass and everything of her when she got up, I was the only one that had noticed and she noticed that I saw and she got embarrassed and then I followed her to the kitchen and she quietly asked if I like what I just saw and I said yes and then she came up to me and pushed my hand into her butt and smirked at me then we went to my bathroom and she had let me feel her up and I fingered her for about 5 min and she said we can continue this later and she said we can let your wife join if she wants and i’m so fucking excited