Sister in-law trouble [M/F]

My sister in-law (I'll say Sue) has been staying with us for around a month and a half while her house is getting renovated. My wife and I have a great relationship with her. She's a few years younger than us we are both late twenties. It was fun having her around doing things we don't normally do the first week. Staying up late having some drinks and talking, going out together. Stuff when it's just my wife and I don't bother doing. We were up late talking one night and my wife went to bed early leaving us alone. We kept talking and soon it drifted to sex. Sue didn't ask much about her sister. I just assumed she knew everything already, they're close. Then she asked me if my wife had any kinks. I didnt give up much but she does have an obsession with being rimmed. She was intrigued and we talked more about that. She asked me what kinks I had and feeling brave and tipsy I told her one I've had bottled up forever. Assplay. I've always wanted it done to me and have never had a partner willing. She was surprised and couldn't believe my wife had a similar kink but never returned the favor. I told her of the one conversation my wife and I had about it shortly after leaning of/fulfilling hers. It fell very flat and we never talked about it again. She started asking what I wanted and if I ever did anything alone and I felt a bit uncomfortable. I gave some quick answers and feeling exposed I did my best to get to bed.

Next morning was a little odd. Felt vulnerable telling my secret to my sister in-law. Worried she might try and talk to my wife about it. A day or so passed and nothing happened. I started to relax but decided not to seek any late night chats alone again. Last Tuesday morning while showering before work someone came into the bathroom grabbed something and on their way out pinched my butt. I assumed it was my wife she's done things like that before. I didn't find out till I was about to leave my wife had already left and it could have only been my sister in-law. I tried to brush it off, harmless joke. Next morning in the shower again I hear the door. I peak out this time and it's Sue. I'm embarrassed and ask if she needs something. She says just needed to grab her brush and she'll be on her way. I go back to showering and try not make something from nothing. Then I feel a hand on my butt, a quick squeez. I turn in time to see her hand withdrawing and hear the door close quickly. I rush to finish getting ready trying to catch her before she leaves but she's gone. Mind racing all day I don't know what to do. I resign myself to confront her tonight tell her to stop and be done with it. I wait till after dinner and get Sue alone. I tell her she can't keep doing that and it's not right. She apologizes and says she wanted to give me some attention after the conversation we had and thought this would be a small thank you for letting her stay with us. The three of us have always had a playful relationship so this didn't seem to farfetched. A little inappropriate but forgivable. I felt very relieved going to bed and glad I talked to her. Thursday morning I am back in the shower. I hear the door and its Sue again and I'm sure my face showed some concern. She apologizes and grabs a brush and slides back out the door. I relax and go back to showering. Not having any of the disturbances like the past two days I take my time in the shower. While washing my hair I hear the door open again. I try to rinse my eyes enough to look but by then I hear the curtain opening I turn and cover myself asking her what she's doing. She pushes me around press her hand on my back. "Bend over." I hesitate "now" feeling exposed I do what she says. She pushes the shower head towards the wall and grabs body wash from the rack. I try and ask her why she's doing this and she tells me to stop talking. I do and hear the click of the body wash cap and then feel it being poured in my butt crack. I try to stand up but she puts pressure on my back and tells me to stay. I do and then feel her finger at my hole. She rubs a little and I start shaking. I feel the pressure as she starts to push and then she's in me. I'm lost as she starts sliding her finger in and out. The feeling is incredible. I've done it to myself before but it's nothing like this. I put my hands on the wall to brace myself as she works in another finger. She works me with a slow pace for at least five minuets. She tells me to cum and I start jerking off. It takes no time at all and I can feel myself contracting around her fingers. When I finally stop she pulls her fingers out, closes the curtain, and leaves. Not a word. I stayed bent over like that for another minuet or so before I finished showering. All day at work I was a mess. I felt guilty, ashamed. More than a little emasculated and a little sore. Sue had never shown a forceful side like that before. I had no idea how handle seeing her tonight. Luckily Sue came home after we had settled in bed and I was glad. I had no intentions of another confrontation like the night before. I tossed and turned all night and finally feel asleep early in the morning. I woke up to a seemingly empty house and was more relieved to have some time to think. I took my time eating not sure who I should talk to first or at all. I shouldn't keep this from my wife but letting this quietly go away felt like the best option. Sue would leave soon and I could just let it go away. I cleaned up breakfast and made for the bathroom. While brushing my teeth Sue enters the door way. I nearly drop my tooth brush. I tell her to leave, I don't want to talk and I don't want her around. "I'm not going to say anything or apologize. You wanted it and the idea turned me on. You get in the shower now I'll do it again you tell me no I'll leave you alone the rest of the time I'm hear." I'm more than ashamed to say I got in the shower. She left while I started washing and soon came back the bathroom. She opened the curtain and told me to bend over. No hesitation this time I turned around and pushed the shower nozzle away as she had the morning before. She had lube this time and the difference from the body wash was noticeable. She worked in two fingers right away and started a slow pace. I was shaking again. Weird conflicting emotions from allowing this to happen and the pleasure that she was giving me running through my head. I don't know how long she did it for but she told me to cum again and I started stroking. Seconds this time and I burst. She held her fingers in while I went and when I was done she pulled out and left. I stood up and slowly washed. Guilty and ashamed now that it was done. My mind raced from stopping whatever this was and getting through the weekend to another morning shower and if it would happen again. Telling my wife floated in and out of trying to remember our plans this weekend and if I was alone at all. I feel guilty and terrible and want more. I know this has to stop and it's petty of me to potentially ruin relationships, multiple relationships in a family for some kink I've wanted. I had to get this off my chest and why not make a throwaway and post here. Because I'm writing this while my wife is shopping and Sue will be home from work in an half an hour and I've been thinking about this window of alone time since my wife said she was going out this afternoon at 8:30am…

Source: reddit.com/r/gonewildstories/comments/32d3mq/sister_inlaw_trouble_mf