All true, but to be fair -the books also focus more on how lonely Robb feels without having his dad/Jon around. Knowing he hasn't done anything yet to save his sisters. Knowing his mom betrayed him in releasing Jaime. And THEN finding out Theon sacked Winterfell and "killed" his little brothers.
Jeyne is the only one who saw this and consoled him, and didn't treat him like a pawn in the game of thrones. Even his mom ignored her instincts to treat him like the boy he is, and kept trying to make him into his father (for show watchers, in the books we only mainly see Robb through Cat's perspective).
So he didn't just fukk Jeyne and marry out of honor,he loved that girl AND believed she was pregnant. His best friend in the world was/is Jon and he knows first hand how much it hurt Jon to be a b*stard. (And Jon, just like Jeyne,is the only person who treats Robb like a normal boy instead of the heir...the Jon/Jeyne naming similarity isn't a coincidence I think).
Also don't forget not long after he not only talks about legitimizing Jon, but he probably set something in motion ( we know he wrote and sent out a letter) to make it happen.
Not excusing him, but the Jeyne move went deep for him. For her too, we later find out she had no idea about the RW and really loved Robb
(for show watchers, Jeyne wasn't at the RW and is still alive in the books...in fact I think she might still play an important part in the game).
LOWKEY the show changing Jeyne to a different person highlighted that they didn't fully grasps what George RR was going for, and George has said that he felt this would come back to bite them in the ass - but he was OK with it because he had a hard on for the actress.
Edit: final thing I'll mention is the show has people fukked up on how old these kids are. Robb is like 16 when he gets killed at the RW, so it's not even insulting to call him a boy - he literally was one.