5D

What circumstances did you think Hero was talking about that may lead Sebastian to withdraw his marriage proposal?

The fact that Hero killed those men.

The ugly gossip that would no doubt go the rounds when Hero's antics leaked out.

The fact that she was held alone with a group of men, possibly raped.

That she showed a great deal more than the behavior expected of a woman of her station...or any woman more than likely...of that day and certainly not the behavior of the wife of a Viscount. Word of mouth could effect Sebastian's role with his peers.

Agree that it was her killing the men but also that she may have been raped first so she was soiled goods.

The fact that she was alone with the men and could potentially have been raped.

All of the above.