Best friend sleeping with girlfriend/boyfriend.

[Omertocracy]

This is slightly misleading.

If it's current (longish-term) significant other, it's most likely them that hurts you more.
If it's an ex, it's most likely the best friend that hurts you more.

That said, any male best friends better not date any ex's. That's a clear violation of the Code, and could cost him his Man Card.

[Powerogue]

I suppose whoever I knew longer and trusted more.

[Valiea]

If your girlfriend / boyfriend sleeps with your best friend, or your best friend sleeps with your GF / BF it's both the same people..

If it was a random nobody sleeping with my GF I'd be pissed.. If it was my best friend sleeping with my GF, I'd be pissed at my best friend depending how best of a friend they were.

Oh ya, I've been single for 6 years -_-

[DeltrusDisc]

Best friend. When it's in the case of having a best friend for a longer time, there's a certain level of respect that should be held.

[Kisho]

My best friend is female. If she slept with my girlfriend, I'd be asking to join in.

[Deleted]

I don't really have committed or dedicated relationships, my girlfriends are mostly physically attractive people that I can have a laugh with, not somebody I'm in love with. I'd probably be more annoyed at the best friend but I can't say I'd be mad for very long.

[Xanjori]

I think Id be more hurt by my best friend in that situation. Your best friend should be your best friend for a reason and you should look out for each other as much as possible.

[Moadar]

If your buddy tells you right away that the girl is a slut then you shouldn't be mad at him, the both of you should just continue to use her for the only thing she is good for.