Why did Ned Stark protect Jon Snow?

Lyanna begged Ned to protect her newborn son, who Robert and Tywin likely would have killed given his Targaryen heritage. Ned promised his sister that he would protect him as she died, raising his Targaryen nephew as his own bastard son at Winterfell, giving him the name Jon Snow.

Why is catelyn so mean to Jon?

Catelyn hated Jon Snow because she saw him as his husband treason. She was really cruel against him because she wasn’t able to explain her feelings towards Ned. Still in the books her behaviour is a unnaceptable when she says that it should have been Jon to ‘fall’ from the window.

Did Ned Stark know that Catelyn still hated Jon Snow?

After all these years Catelyn still hated Jon Snow. She can’t accept him as a son. It didn’t mean she hadn’t tried but she was just not able to do it (She had conversation with Talisa Stark about how she is not able to accept Jon Snow as her own son) Ned Stark knew that Catelyn hated Jon Snow.

Why didn’t Eddard Stark marry Catelyn Stark?

Because Eddard did not trust Catelyn at the time enough to tell her about a secret that could lead to murder of Jon and destruction of House Stark. Later the topic just never came up and both of them decided not to bring it up and enjoy a loving marital life. Nothing was to be gained except guaranteed security of Jon. Just a precautionary thing.

Why could Ned not trust Catelyn with the secret?

Ned could not trust anyone with the secret as if word would come back to Robert it would likely end with the death of Jon. Early on Catelyn inquired about Jon’s mother based on rumors she was hearing in Winterfell. After Ned denied her, she stopped asking…

What does Ned Stark promise to do to protect Jon?

Ned is also an honourable man and he promises to protect Jon: You have to protect him. Promise me, Ned. Risking anyone finding out that would mean Jon’s death as Robert wants all Targaryens dead. It would also most likely mean Ned’s death as he was harbouring that secret and actively protecting him.