Having just read the whole thread, I'm wholeheartedly with AF on this.
I'm usually quick to be irritated by double standards between men and women on here but, on this occasion, I'm not. It's not relevant as it is a person who is being discussed in a specific set of circumstances and not a 'man' or a 'woman'. Although, for the record, I would extend the same following consideration to a close male friend too.
We don't know exactly what is going on for this woman, but the OP knows that she has been having some difficulties recently. What she actually knows may be the tip of the iceberg. After all, "a rough time" could be anything from he forgets to take the bins out to the relationship is falling apart and she's devastated to abuse.
Having been in extreme psychological distress myself at different points, and seen it in a couple of people who were quite close to me, I would want to find out if this was something that applied to them before casting them into the social wilderness and ostracising them completely, as it can make people behave in ways that would otherwise be unacceptable and uncharacteristic and to abandon someone at a time like that would be unbelieveably cruel.
This behaviour is clearly out of character for her, or she wouldn't be the OP's best friend in the first place. If my best friend, male or female, behaved in a way that was both appalling and unacceptable, I would want to find out they were ok first and then take it from there.
All other posters might be right. She might just be an attention seeking bitch who didn't care that she was hitting on her friends' husbands/boyfriends/partners and holds them all in utter contempt, having no regard for them whatsoever. Or she might be in such a bad place mentally and emotionally that she hadn't fully processed what she was doing at the time.
I think a lot of people react so badly when it comes to things like this because they are projecting their own fear of being cheated on/their partners being tempted/it happening to them.
I don't have a whole lot of close friends, but I know that if any of them did something like this, it would be completely out of character and my first response would be concern for them and not indignation/anger.
If she laughed in the OP's face and told her that the boyfriend clearly wanted her blah blah, then, yeah, I'd tell her to fuck off. But I strongly suspect that isn't what would happen here.
And if a male friend ever did similarly, I would hope we'd all evaluate the individual situation on its merits and not just issue a blanket decision regardless.