I have made my feelings on Loki’s behavior quite clear, that he has taken no consistent responsibility for them instead only gives excuses for why it’s not his fault, how Loki is cruel to those around him, lashing out in his anger and childishness, etc.
But sometimes I do want to set that aside and look at where it comes from (not that we have anywhere near enough to really say about that, we know so very little about Loki’s actual circumstances or things that are going through his head) and try to look as honestly at the character as I can.
And one thing I think you can say with a fair amount of certainty—Loki was deeply unhappy at this point in his life. Whatever he chooses to do about that unhappiness, setting that aside, it’s still true that it’s not at all hard to find moments where it’s not even anger that seems to be the predominate emotion (though, that’s there, too, given how much of it comes bubbling up so easily, the moment things don’t go according to his plans), but just that he looks severely and terribly unhappy.
He looks like someone who constantly swallow their feelings, rather than expressing them (and this is why he explodes so hard in The Avengers, because a lifetime of bottling emotions, when you finally let them out, the last thing you want to do is be reasonable or put the cork back in, to go back to constantly struggling to hold it all in, not when it feels so much better to just pour out all this seething rage, no matter how fair or unfair it is), he looks like someone who feels things so terribly deeply but doesn’t know how to express himself in a healthy way.
I think it’s not entirely unreasonable to assume there was probably at least some dismissing of his concerns, if he raised them—when he expresses himself to Sif+W3 after Thor’s banishment, they accuse him of jealousy. The thing is, while that’s easy to see from Loki’s point of view that they’re dismissing him, that they’re not listening to him, that he has really legitimate points and they’re dismissed, which is partly true!, while that’s true, it’s also partly true that Loki is jealous.
He didn’t plan for Thor to be banished, but planned for Thor to be lured into this bad situation, then he took advantage of the situation when it was placed in his lap.
It’s easy to understand that Loki looked at the situation around him and saw the closing window of his one chance to prove himself without Thor around, that already their friends were clamoring for Thor’s return, that already they overlooked him so easily and only wanted Thor (in Loki’s view), that Loki measures himself by Thor (this is not Thor’s fault, btw, this is something that is Loki’s issue and laying the blame for it at Thor’s feet is just as much making it All About Thor as the original problem), so the ticking clock over his head pressured him to jump at this chance.
This chance to take the reins and deal with Jotunheim and prove himself. I genuinely believe Loki only wanted the throne because Thor wanted it (because he measures himself against Thor, defines himself too much by Thor) because he wants to be seen, as he feels he’s not seen enough. He’s deeply unhappy and thinks that getting praise from other people will fix that.
And external validation can be really helpful in building yourself up, who doesn’t feel better when praised? Feeling overlooked can make anyone feel unhappy, like you don’t matter or nothing you do is good enough. But Loki’s problems run a lot deeper than that and I think just looking at him in these moments, where all this unhappiness practically radiates out of him, I remember that I do hurt for him and wish desperately for him to find a way to get back on a better path.
I think these moments are when I most relate to Loki, as someone who has often been unhappy in my own life, as someone who has felt not good enough. It’s difficult for me to separate Loki from the idea of mental health issues and looking at him here, it’s really easy for me to put him together with the idea of depression.