This of course is easier to get if you are into the comics, like me. But I do give you that the script was a little sloppy in those points, especially because they deleted several scenes that helped to get into Loki's character psyche (like you pointed out that would have helped)
Yeah, I was just ... lost. There were chunks missing and thus the character came off as really poorly written, in a poorly written story. Which is a shame, because Tom Hiddleston is a good actor and it could have been a fantastic movie, if only the script had been better.
I mean, the fanfic is doing a wonderful job of fleshing out Loki's character and bringing in stuff from the comics and filling in the gaps. I get that his motivations are supposed to be proving himself as a son worthy of Odin and the throne and all that jazz and being jealous of Thor. But ... that didn't happen in the movies. It was kinda like they waved their arms and went "blah blah blah! Explosions!" and thought we wouldn't care.

Also, I understand that you right now don't like him because he made Thor cry (admit it, that's the mayor problem you got with him right now, hahaha)
Well, that was the moment he lost any sympathy he'd gained from me. Outcast smart guy surrounded by bros? All my sympathy. Total dick who tells his brother their dad is dead and their mom wants him to stay away from home and he's not allowed back home in their universe EVER AGAIN ... when simply saying "Father thinks you should stay put for a while, I'm trying to convince him to un-banish you but it'll take some time" would have sufficed? Yeah, all that sympathy = GONE. There's being evil and entertaining and then there's just being plain sadistic for the lolz.