The void
He has lost himself, the minute he knew the truth of his parentage.
He has lost himself to lies, to a whole lot of delusional world in Asgard, an illusion he has lived in and for, since as long as he can remember.
He has lost himself to the cold and bitterness of Jotunnheim.
He knows he used to be something, someone but who that someone was? He will never remember.
He wonders, should he have known the truth.
Truth was a resolution to the whole tangled mess of a question that has been raging through his mind, Why was it always Thor? Why is it always Thor? Despite he was smarter, despite he was wiser, despite he was more efficient, more fit.
Sure, Odin will never love him as much as his biological son, let alone the fact he was no mere ordinary adopted Asgardian, he was a frost giant, the enemy, the monster they scare children with at night.
But truth meant all he is, all he was, was a very big slander, an Illusion much like the one he creates himself.
He didn't belong to the world of Asgard.
He will never belong to Jotunnheim.
He belongs to nowhere.
He knows Laufey would have never been as half a good father as Odin was to him.
He knows that despite Odin's preference to Thor, Odin loves him.
He knows that Frigga loved him and Thor with equal measure.
He knows Thor loves him as well and he loves Thor, he loves his brother, despite everything, despite the pranks, the rivalry, despite the truth.
And there lies the core of the problem, there is the tight knot.
He is flinging on a very fine line, between loving them, between appreciating the fact they kept him alive and loathing himself, loathing everything he is, acting like the monster he was born to be, destroying everything and everyone he touches, destroying the big unreal fantasy he has been living in.
He doesn't want to feel any more.
He doesn't want purgatory, he doesn't want redemption.
He used to have a lot of dreams, when he was a child.
He later learnt dreams lead to nowhere.
He used to want the throne of Asgard, very much.
He doesn't want it anymore.
He just wants an identity, any identity.
He knows he will never get one.
So all he wants is to be forgotten.
He wants all of them to forget his existence, he wants to forget his own.
So when he and Thor are clinging to Odin's staff, he chooses the easiest way out of the mess,
He doesn't put Odin through the hard choice.
He doesn't torment the man he wishes was his father, the man he owes much.
He doesn't act as the liability he always was,
He lets go.
He descends to the void, to where he belongs.