Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: Despite the fact that this happened several years ago now, I still feel like an asshole because of all of the drama that ensued from this event.

So. I was out drinking with a friend. Let's call him M. M divulged that he had cheated on his girlfriend a few times with someone who lives in his hometown while he was visiting his parents. He likes exploring different partners, but he wants to someday get married to C, his girlfriend. He stressed to me that I shouldn't tell C. 

A few weeks later, I was talking about this occurrence to my friend who I'll refer to as 'S.' I was asking S his opinion on whether or not I should tell C. In hindsight, I probably shouldn't have told anyone better yet S, but C has mentioned being rather unhappy with C. After years of being mistreated by M and feeling fed up with his crap myself, I thought maybe C needed to know. However, S told me to leave it alone. I thought it was all done and thought nothing more of it.


 Later that week, we were all at a party together- me, C, M, and S, and some other friends. S begins to hit on C. It seemed casual and in somewhat good fun, so I didn't think too much of it. At some point, I got too drunk, so I went to go take a nap. While I was napping, S sloppily confessed his romantic interest to C and then told everyone at this party that I told him what M said to me that night. He wanted to 'save' C from M. 

The night ended with C breaking up with M (to be expected). As a result, M and I are not friends anymore (which was also be expected and frankly, I'm fine with), and I don't really talk to C or S anymore either. However, I lost almost all of my old friends who hang out with M, as they all blame me for splitting the two of them up.

AITA? 

telling my friend's girlfriend that he has been cheating on her