It was well written because it showed his humanity. Many princes and kings have made questionable moves over a woman. Wars have been started over women.
Robb, like everyone else, didn't have his father's honor. Literally no one in the world had Ned's honor which is a backbone in the show and why that world is the way it is.
You're looking at this from a modern point of view.
Robb was raised in the aftermath of Robert's Rebellion. He'd know the dangers of taking betrothals lightly.
He was also clearly at least 20 in the show.
He was a king at war, against a family with more men with better armor than he had.
Marrying a traveling nurse gaining nothing, is the stupidest thing he could've done, and Robb was never said to be stupid.
And it legit surprises me that you're defending that bs, since it speaks to how little the showrunners respected viewers intelligence, that they gave us that.
Human is trying to have your cake and eating it too.
Human would've been to sleep with her, taking her as a mistress while also marrying the Frey girl because she came with 4k men.
There was no logic behind that development. Nothing in regards to how his lords would react, what marriages any potential children could possibly make since their mother is damn near commonborn.
The writers gave us a lump of dry doodoo, and you're calling it gold?
Nah b.