@MeiraEve
Probably a baseless accusation he wanted to make real, hence he sent the thugs, keep in mind in classical society even a accusation could ruin your chances at a future, basically the first prince comes off as scum to me that has a good public face, while the ML has a rather bad rep but doesn't lie or do anything truly wicked and is essentially the opposite, a hero with bad publicity.
@Lioness94
See above, the heroine might be black hearted, but the prince is the one who sent the thugs with the purpose to ensure he wasn't found out, so it's likely at least so far, this is all first prince.
@kayd
Possibly, but considering the stuff he'd do to save face, i think she's better off without him.