My sister is betraying her husband. Should I tell him?

Dear AmoMama,

I'm between two fires and don't know which way to turn. My younger sister is married to one of my oldest and best friend and now I've discovered she is cheating on him.

Two years ago I moved back into town from LA and bought myself a lovely little condo, but since I travel a lot, I left a duplicate set of keys with my sister, so she could go in when I was away and water my plants.

A week ago, one of my business trips was cut short and I came home a day earlier. I walked into my house and immediately noticed that something was off. There were wine glasses in the sink, and I always leave everything very tidy.

As I walked into my bedroom I saw my sister on my bed with a man, and when he turned around I saw it was not my brother-in-law.

The man looked very embarrassed and got dressed and rushed off, but my sister was cool as a cucumber and she just sat there on my bed with this insolent look.

I asked her what the hell she was doing, and she told me she "was getting some" since her husband worked all the time, and got home "too tired".

My sister does not work, and her husband lavishes everything she desires on her. I could not believe my ears. He had been my best friend since primary school, and when he married my sister it just made us closer. He is like a brother to me, and she is cheating on him.

My first impulse was to drag her out of that bed and give her a shake to wake her up, but I could see it was useless.

I've told her if she does not stop, I will tell him. She laughed and said she knew I'd never hurt him, she said if I told she'd tell him their son is not his, and that would break his heart.

I want to protect my friend, but should I betray my sister and maybe hurt him even more?

If you need help or advice, reach out to us, and thousands of women just like you who are struggling with the difficulties of life. You are not alone, we are here for you, and we listen; so write to us anonymously using this form.