I Had No Idea

My nephew and I are only a few years apart and we are close. We do a lot together and we knew almost everything about each other. At least I thought we did. He had been secretly dating a girl never brought her sound didn’t mention her at all. I don’t care what or who he dates what ever. There is a girl who I guess we call FWBs Karly her name half Mexican girl she’s 26 fit ex dancer long legs bubble butt gorgeous face. Have known her for years and my nephew knows this. He also knew that we Karly and I on many occasions have had sex. Now juts sext but wild hair pulling rough ass slapping sex. He never told me that he and he that gone out a few times. I would have definitely not called her over on a random Friday night to come hangout. When ever I call Karly to come hang out I 100 percent expect her to come over and fuck she knew this and has never said no. Even when she was dating other guys that I knew nothing about I called and Karly came and I cum. So I text her Friday night her corn over and wear something sexy. She responded with a pic of a g string. She shows up she has heels on a coat takes it off and she’s in heels a g string then turns bends over and shows me an ass plug that she purchased with her very own money. I put a good hurt on her and we pass out. Saturday morning comes around and my nephew shows up and as I’m talking to him here walks out Karly half naked says hi and says she is going to shower. My nephew storms out all list off. I’m like dude what’s up he stops and says you have to fuck the one girl I’m trying to date don’t you. I honestly had no idea they where dating neither one of them mentioned anything to me. I look like and feel like and ass. I asked Karly if they where dating she says no just having fun. So I’m at a loss for words on what to say or do. Karly never left my place laid around in her underwear and we fucked a few more times. Am I supposed to stop banging her ?