Very difficult situation here
Jeez MM, that's a horrible situation to be in. On one hand you've got your conscience and anger at the situation telling you that you cannot simply do nothing, while on the other you'll be aware that if you do spill the beans to the wronged party and her partner rescues the situation then all her anguish will be directed back at you.

I don't envy you one bit, I suppose the best thing you can do is be there for the girl if/when she finds out. In my experience, people's disrespect for their partners seldom goes unnoticed for long.
(Bicycle Repairman "you're also a bit of a wanker", Mon 29 Sep 2008, 14:38, Reply)