@Kraeth "I thought something unexpected was going to happen but those smirks tell me it's all according to keikaku."
Not sure if this series covered it previously or not, but to explain the pleased expressions in the final panel, traditionally the noble house breaking an engagement would be the one responsible for palimony/compensation (and usually a sizable amount, since it involves the "face" of the house in question). Our protagonists were planning on putting the responsability for the break on the fiancee due to his conduct (ie, "yes, we're the ones breaking it off, but it's not actually our responsability despite that, because of these reasons, so we should still be the ones getting compensated"), but now that he put the responsability on himself to begin with, they can potentially obtain a higher compensation (as they no longer have to leverage the circumstances to put themselves on "the right side" of the break, meaning they can instead leverage it for additional compensation).