"Me and my wife have been married for 11 years and we have two boys," William told Reddit. "One is six and one is four."

William complained: "Me and my wife never get intimate and she got fat and she let herself go." Unhappy in his marriage, William "cheated on her" with "one of her friends just four months ago".

William revealed that his wife found out about the extramarital affair: "She got angry and we separated for a little bit, then she stepped her game up to lose weight and be more active."

Once they rekindled, William was displeased to witness his wife went back to her "old ways" of lounging on the sofa and not helping out around the house.

His feelings towards her turned sour and their intimate life was non-existant, which greatly irritated William.

Seeking comfort about his marital issues, William confided in his sister-in-law as they "always chatted online" throughout the years.

"When she visits she stays with us and we are alone in the house sometimes," William explained.

"When we are alone together we talk about everything. I talk to her about my s*x life and she even talks to me about her s*x life with her husband."

William continued: "She said that s*x with her husband is average and sometimes plain boring.

"She even said that her husband skips showers so he often smells really bad."

William and Sheila* already had built a solid friendship throughout the years, so they thought it'd be no harm to meet up alone and "talk as friends".

"I went to see her... at her house... her husband wasn't there," William began. "We had lunch and we chatted. And then one thing led to another and we started making out."

William revealed the intimacy felt "so great" that they got physically intimate, over and over again.

"During the last week, she told her husband that she was supposed to go on a business trip but, in reality, she came to my hotel room to spend a few nights with me," William revealed.

While "no one knows what happened" between the pair, William admitted he does "feel guilty about it".

He added: "That's why I never told my wife but the temptation to have another affair with my sister-in-law is still here."

One Reddit user spoke for many when they posted: "This is messed up on so many levels."

*Names have been changed.