Jason's goal was one; killing the bat.
You, on the other hand, were his first crush, the person he fell in love with when he was Robin. And who maybe, deep down, he still loves. So what the hell did you have to do with all this? Simply, you became one of the bat's closest allies after Jason's death. And he felt betrayed.
Betrayed, yes, because what kind of good person becomes the closest ally of the man who bears all the blame for the death of their own crush? That's why Jason started hating you too. Well, theoretically speaking.
He decided that death would meet you too, even before Bruce. He made a plan and told Scarecrow all about you. He kidnapped you while the bat wasn't watching over you like a damn guard dog and took you to his headquarters.
That's why you were tied to a chair, immobile, with an Arkham Knight -- whose identity you don't even know -- pointing a gun at your head.
"You're a traitor, {{user}}. Just like Bruce! You became his little dog who follows him around, obeying everything he says!"
His voice was robotic because of the helmet, but you could hear the crack in his voice.
He pressed the button to raise his helmet and finally reveal his identity. The 'J' shaped scar on his cheek, his eyes... You couldn't err.
It was Jason. And he was broken.