It almost crosses into Nightmare Fuel that the Allfather is implied to be willing to let his favorite and firstborn son be killed to stop him from defying him. When he is informed of Thor and Loki's escape, he tells the guards to stop Thor "by all means necessary". He becomes completely bloodthirsty, not caring how many Asgardians might fall defeating the Dark Elves. That hope no longer exists to protect you.
You should know that when we fought each other in the past, I did so with a glimmer of hope that my brother was still in there somewhere. Loki: What makes you think you can trust me? There's that split-second where Loki's eyes widen from the realization-that here is his brother who never fails to see through him and his true feelings, and that there really is no point in pretending when it's him-before he drops the act and we see him broken in the corner with his cell in shambles, having violently grieved over Frigga's death offscreen. When Thor visits Loki in his dungeon for the first time to ask for his help to stop Malekith and Loki is all tough and defensive towards him, he tells Loki to drop his illusion.
Frigga's death is the trigger for him to launch his belongings across the room by just closing his fist. Even more tellingly, this is the first time we see Loki overtly using his power for anything other than illusions. He was not allowed to go or even see Frigga's funeral, despite Odin knowing how much Frigga had meant to him (which is hardly unreasonable, since Loki is a dangerous and unrepentant criminal - and that somehow makes it worse). Loki waits for the guard to leave before standing. We don't hear what he says, but we can guess. Once the boat is lit by a fire arrow, all the other boats are lit. Knowing they've come for Jane (whom Frigga is guarding), he whispers "Frigga." Before this scene, Odin realizes that it's the Dark Elves invading.Then Jane arrives and can only just stand there in shock. She's killed, and only a second later, Thor comes running in, managing to, at minimum, scar the right side of Malekith's face. Even if a lot of people already knew it was going to happen, it was still heart-wrenching. This is even sadder when Frigga dies only hours later. At least Loki looks sorry and tries to apologize before Frigga dismisses the illusion, as if to say "I didn't mean it like that, I'm sorry". Then there were the hands, the tears in both their eyes, and the reveal that she was using her illusory self to visit him.He has completely given up on ever gaining his father's approval. but the expression on his face when he delivers one of his lines clearly speaks to a deep well of bitterness and regret. When Loki is first brought before Odin, he falls back on his old banter pretty quickly. It's truly heartbreaking to see that, between then and now, any affection that Loki once had for Odin is now entirely gone.