Meximama
I found out a few days ago that my sister in-law is cheating on my older brother going on 6 months with a neighbor in their apartment complex.

He makes all of the money in the marriage while she sits at home or is her neighbor's place doing the deed. If you think it couldn't get any worse the guy is  18 while she is 33
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Kiki
In my opinion you should tell him.  If it were my family memeber that was being hurt I would definitely tell them.  I couldn’t sit back and watch the destruction. Think about yourself, would you want to be informed? You would be acting out of love and concern. That can never be wrong. 
D-Day#1 Dec 19, 2017
D-Day#2 Jan 13, 2018
5 year “on/off affair”

Married 25 years, together 35 
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Keepabuzz
Absolutely, without a doubt you should tell him. He is your brother. The truth will eventually come out, and when it does he will be cut even deeper knowing that you knew and didn’t tell him. His health is at risk, who knows what younger man (and I use the word man very loosely) has or passed on to her and then to her husband. 
Male BS, D-day July 2015, trying to stay out of the dark.....
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ThrivenotSurvive
I agree with the above.  If you worry that your brother could hurt himself or someone else, than ask for help from friends or family to keep an eye on him.  But otherwise, I don't think you should delay in telling him.  If I had found out close family or friends had known and not told me - I would have been devastated and felt betrayed by them as well.  

Don't make the mistake of thinking you are protecting him.  You aren't - she could be passing on diseases, getting pregnant with the other guys baby - or your brother's - the list goes on and on.  Protect your brother.  ASAP. 
BS - Female
Married 27 years, one adult child
DD May 2016

“When we are no longer able to change a situation, we are challenged to change ourselves.” - V Frankl
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Vanessa
Tell him NOW
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Meximama
Keepabuzz wrote:
Absolutely, without a doubt you should tell him. He is your brother. The truth will eventually come out, and when it does he will be cut even deeper knowing that you knew and didn’t tell him. His health is at risk, who knows what younger man (and I use the word man very loosely) has or passed on to her and then to her husband. 



Yeas thats true
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Meximama
I agree with the above.  If you worry that your brother could hurt himself or someone else, than ask for help from friends or family to keep an eye on him.  But otherwise, I don't think you should delay in telling him.  If I had found out close family or friends had known and not told me - I would have been devastated and felt betrayed by them as well.  

Don't make the mistake of thinking you are protecting him.  You aren't - she could be passing on diseases, getting pregnant with the other guys baby - or your brother's - the list goes on and on.  Protect your brother.  ASAP. 
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Meximama
I just dont want him going ballistic and trying to kill that kid.
But ultimately this cant go on
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Damaged
Please tell him now! If he finds out the you knew and didn’t tell, he will probably consider this a double betrayal. What if his wife becomes pregnant? What if it’s OM ( other man ) child? Do they have children? If so, he should DNA test them. This may not be her first rodeo. 
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Blessedby7
I absolutely agree with what others have said, especially about him feeling betrayed by you as well if he finds out you knew. Many of my husband's friends knew about his affair. They knew him, and the other woman, but didnt know me. However, I still feel betrayed by them. They could have easily found me and told me, or at least told me something was going on,  but they didn't.  And that hurts. It would be SO much worse if it was someone I knew or a family member. 
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Keepabuzz
One condition of me even considering giving my wife an undeserved second chance was that every friend that knew what she was doing, was to be cut out of both of lives. She didn’t really want to lose her friends, but I made it clear. It’s them or me, actually it’s them and for sure not me, or not them and maybe me. Choose. It would have been no different with my if my sister knew, and did’t tell me. I would literally have never spoken to her again. She would be dead to me. 
Male BS, D-day July 2015, trying to stay out of the dark.....
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Kiki
Tell him!!
My two sister in laws knew about my H’s affair, for years.  They even went on a trip together.  They are no longer in my or my daughters’ lives.  I want nothing to do with them and my daughters have nothing but hate and disrespect for their aunts.
Dont risk your relationship with your brother for someone who is willing to cheat and lie for their selfishness.
D-Day#1 Dec 19, 2017
D-Day#2 Jan 13, 2018
5 year “on/off affair”

Married 25 years, together 35 
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Meximama
Hello ever yone thank you for the replies.
Sorry for the late reply.

Unfortunately I fell sick the last two days.
Now Ill read.
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