Loki

Loki has just recently come back from encountering a man named Thanos for the first time. He was found in the land of the Frost Giants when Thor came looking for him. Loki himself was pretty bruised and physically broken, but it was more or less the mental brokenness that affected him.
Meanwhile, Thor and Frigga know that Loki is hiding something terrible from them, and even Odin begins to worry that something must have been done to Loki that was worse than they had previously thought. Loki tries to hide his secret, thinking it better for the only person that it is known around Asgard that he cares about-his adoptive mother Frigga. Little does anyone know, Loki trusts Thor immensely, possibly even more than Frigga.
Thanos wishes to take revenge on Loki, for managing to escape, and not agreeing to his terms. So far, nobody within Thanos's circle, including Thanos himself, knows how deeply Loki cares for Frigga, nor how far his brotherly affection towards Thor goes.
Everyone knows Loki is hiding some sort of terrible secret, but will Loki be able to be tricked or coxed into telling anyone what the problem is, or will he continue to distance himself from everyone until there is no going back? Most important, will Thanos actually get his revenge?