A young woman on Reddit is furious her family has been keeping her brother's infidelity a secret from his fiancée — who is her friend — so she plans to expose him.

"Now one of the fiancée's big things is that in the first couple weeks of the relationship she caught my brother talking to other women, and she made it known that if it ever happened again, she would leave," the woman began.

"So then I found out the context of my brother's infidelity, which my parents don’t even think is infidelity because nothing actually happened. But it was found out through one of my mom‘s friends that my brother had been messaging her late at night for three months talking about hooking up, and she kept rejecting him. Then when his car broke down, he would get rides with her frequently. And I guess he was touching up on her one of the last rides that she gave him. She finally told him off, and then later that week she called my mom really drunk asking [if] my brother and his fiancée were still together because of his actions," she continued.

Instead of encouraging her son to come clean, though, the mom urged him not to reveal his philandering ways.

"When I found this out, I was very angry. I was angry at a lot of things, but for the most part, I was most angry about the fact that my mother wasn’t pushing him to tell his fiancée and was instead telling him that he needs to control himself better ... My brother was being let off the hook and not being held responsible. I was angry at the fact that he was acting just like our deadbeat of a dad, and I was pissed that I gave him so much credit just because he was my brother," the woman explained.

Not long after, she pressured her brother to do the right thing and tell his bride-to-be, but he didn't react kindly to her recommendation.

"When I was telling my brother about the boundaries that he had broken and the way he had been acting and the actions I was going to take if he doesn’t take responsibility, he told me that if I did this, I would no longer be his family, and that he would never once talk to me, see me or ever be in a room with me ever again. He said that me and my mother need to worry about our own boring lives and to stop meddling into his relationship," she recalled.

"So I snapped back and told him he has a week to tell her or else I will. And then I left. Now my mother is telling me I can’t do that, and that if I do this I will be tearing my brother's world apart and it won’t make him take accountability but instead he would just shift the blame onto me," the woman concluded.

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User reactions in the comments section were a mixed bag.

"You didn’t go behind his back, you’re giving him fair warning to do the right thing and come clean before you do it for him. Maybe his soon-to-be ex-fiancée will soon need a roommate, far, far away from this drama," one person suggested.

"Yeah, this is a mess. Yes, cheating is bad. But, I would have talked with him about the info you have and your concerns and the spot you're in before being the one to tell her or giving him an ultimatum," someone else commented.

"You're her friend, you have the right to tell her to minimize her suffering. And your mother has the right to not push your brother to fess up, it's his relationship to manage. I can see where his actions are situational; some couples would be fine, so I can understand your mom staying on the sidelines," another wrote.

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