TELL TELL TELL
This is no where close to the severity, but it is along the same lines.
My friend and I were dating two guys in the same fraternity. One night at a party, that she was not at, I saw her boyfriend kissing another girl. I decided it was best not to tell her, after all it's none of my business...right? Well he broke up with my friend shortly after that. Two days after the break-up one of his brothers came up to her and said "What did you say when Sarah(me) told you about him kissing that other girl."

She came back to me and wanted to know why I hadn't told her. I told her I wanted to spare her feelings, and I honestly thought I was doing the right thing. UNTIL
That summer my boyfriend went home and so did my friend. I stayed at school for summer term. Every summer there is a huge festival down by the river. There are thousands of people who attend this event. They both went but not together. Then that fall he gave me a lavalier I was very excited. I told all my sisters at meeting and then went home and told her (she is not in my frat). She struggled with the words and finally told me that she had seen my boyfriend at the river with his ex. I was in total shock. I didn't say anything, I knew I had no room to be angry and I knew it was her private way of getting me back for keeping a secret from her. I know now why she was so angry with me.

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Remember to learn from others mistakes since you don't have time to make them all yourself