About how you’d control the Freys if you were Robb strategically planning to break the marriage vow: Robb can’t forcefully arrest Frey for planning to break his vows: remember that Frey kept 400 of his own men back to garrison his castles, Robb 0only matched that number, so he didn’t have enough power to overwhelm those guys; and Edmure actually pulled the northern forces OUT of the Twins almost as soon as Robb marched west; and the Freys weren’t even thinking of defecting till then