Wife's Slutty Niece

So i have a niece by marriage not blood. she's 24 and likes to flirt and likes to get touchy. Sydney, is without a doubt a spoiled brat but very hot and attractive. She flirts with me when know one is around. she will try and squeeze by me in the hall or kitchen and stick her ass out and grind my cock a bit and she would just say wups and has even given my the "blowjob sign" before. Now i have told her before that i don't think she should continue this behavour as its kinda wired but she seems to not have a care about it all saying "its not like we are blood family" nevertheless i told her to cool it. A few weeks later my wife and i were asked to house sit and feed the cat as the family was gone for 3 weeks. Obviously the wife and i take care of the house and cat and use the hot tub they have everyone in a while. The one night the wife didn't want to go over so i just went to relax for a bit after feeding and cleaning up that cat litter box. i texted the wife saying I'm going to stay for a bit and hit the hot tub. While I'm in the hot tub i hear a door open and close and who do i see walk past the window in the kitchen...Sydney. Now i mumble to myself ok time to go but as I'm about to get out she opens the door and ask's hey you wanna beer and i said no i was just getting out to go she says come on man I'm having one just stay for one so i say fine just one. 10 minutes go by and she come out to the hot tub in a thong with my beer. Now i don't remember if i said this in my head or out loud but it something around a "holy fuck" and i remember her smiling. She got in a gave me my beer. For the first while we just sat and talked about regular stuff nothing exciting. I finished my beer and said ok time to go and stood up to leave and out of no where she says " you know my aunt tells me you like giving her facials" and i just stood there thinking what the fuck do i say to that and all i said was "yeah well your aunt says a lot of things so you know" Syd reply oh so its not true? i was just saying because i like a good facial every once in a while too. At this point i just cave telling her yeah your right i do like cumming on your aunts face so what and she flat out asks me "do you wanna cum on my face"? and that was the breaking point for me replying "fuck i would love to cover your face" i get back into the hot tub and she stands up telling my to eat her pussy and ass first and i do not hesitate at all. i tell her to lay down so she is half in the hot tub and half on the deck so i can stay in while i eat her pussy. i go to town on her pussy and made her cum 3 or 4 times i keep going but she stops me saying thats enough. I slide her back into the hot tub with me and bend her over sliding her thong to the side while i bury my face into her ass licking her rim and hole plunging my tongue into her asshole repeatedly. she is moaning and moaning saying i love it again and again and to keep going. At this point its a free for all and not evening caring about my marriage and i keep going on her. Suddenly she says you can if you want to while her cheeks are spread licking her ass i ask want to what? and Syd says "fuck it" you can fuck my ass if you want to. I paused for a second then saying i have never fucked an ass before and she replies its ok i like anal. Are you sure i ask? her reply oh yeah just use a lot of spit. So i bury my face back in her ass for a couple minutes and say ok i keep her bent over spit on her asshole i slowly push my cock into her asshole. she lets out the biggest moan like she is just loving it. So obviously as i am new to this i am going slow but she says just fuck it do what you want and fuck my ass and thats exactly what i do. i bare down on her with long hard thrusts for a couple minutes and then stop and pull out. She asks are you ok? i go yeah i just don't want to cum in your ass i want to save it for your face, she giggles say of course. she takes a hold of my cock and starts sucking it like a fucking champ. all of a sudden i get a call from the wife i tell Syd to stop while i answer the wife ask's hows everything there and the soak i just say everything is good and I'm just about to finish up and head home we hangup. Syd get right back on the cock trying to go as deep as she can practically coking herself which was fucking amazing. I tell her you suck cock better then your aunt. Im almost there about to cum i tense up Syd says the magical words i pull out of her mouth stand up she opens her mouth moves her hair out of the way and i explode all over her face just ropes of cum cover almost every inch of her face dripping onto her tits and in her hair she doesn't want to open her eyes obviously but i put my cock back in her mouth and she sucks a little more getting it all out. Syd was shocked by the amount of cum on her but yet was super happy about it. i helped her out of the hot tub and helped her get cleaned up. We talked about what just happened and that this should never be spoken about again to anyone for any reason. i definitely felt bad about it after but at the same time my wife would never do that kinda of stuff so i chalk it up to a once in a lifetime fuck session is all. i just hope know one ever finds out EVER!