I often see what I call the “Can’t say ‘I love you’” trope applied to Loki in Thorki fics. This confuses me. Loki’s said “I love you” to Thor in canon, and told others he loves Thor.
It’s actually Thor that’s never said the words “I love you”. I headcanon he can’t, not because the commitment is too great (as is most often the case when a character can’t say “I love you”), but because the sentiment is not enough. The words “I love you” get used by so many others, often carelessly. They do not begin to describe how Thor feels.
I admit I’m guilty of this, and I think it’s a matter of over-identifying with Loki. I have a lot of trouble saying “I love you” even to family members. But of course you’re right that Loki doesn’t have this problem in canon.
I do think I characterize Thor in a way similar to what you describe. He has all these worshipful thoughts about Loki but he feels like he can’t say them out loud because Loki would laugh at him.