Robb didn't understand what honor was in the feudalism system.

The feudal system was a system of reciprocal relationships with lords, their vassals, and the land the vassal's lived on. Robb spat on the culture of feudalism by thinking one women's honor was worth more than the feudal contract he signed with Walder Frey, when Walder Frey demanded that their houses be joined in exchange for the possibility of his house be extinguished by turning traitor by fighting against Joffrey Baratheon.

A lord and his oath to his vassals that is what the feudal society considers important for without trust between a lord and his vassals there was no feudal society. Instead it was just war and revenge.

A honor system is what the feudal system did to try to reduce war (similar to Hobbe's state of nature), if everyone in the system fulfills their reciprocal obligations and does not offend each other the area would be at peace.

Robb had it coming when he broke the sacred vow. If he wanted to take care of Jeyne Westerling's honor after "defiling her" (I am using a pejorative word on purpose) he should have taken her as his concubine and treated her and his family well, give them land and titles as king this was in his power, if need be marry Sansa to one of the two Jeyne Westerling's brothers or marry Rickon to Jeyne's Westerling younger sister. For sake don't marry her.

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I find it ironic that with the etymology of the word "honor" its main definition arises during the feudal period of England and France, while a "women's honor" refering to a women's maidenhead didn't arrive until 200 years late during a time when feudalism is almost extinguished.