It was love at first amputation. Robb had just defeated the Lannister army at the Battle of Oxcross when he came across Talisa, a non-northerner who was in the midst of cutting off a man's infected foot. The rest, as they say, is history (or tragedy). Robb irresponsibly rescinded his agreement to marry Walder Frey' daughter -- after gaining access to the bridge he needed, of course -- and eloped with Talisa instead! His mother was thrilled, as was Frey.