I do not know the song but I think if you consider it literally: He is playing a game of dominoes with his girlfriend but is pre-occupied with their failing relationship - his mind is on other things [gone astray]. As a result, he is not concentrating on the game and, as a result, he loses.
It could also be a metaphor for their relationship - perhaps he ...
There is overlap in the meanings and it depends, to some extent, on whether you are using AmE or BrE.
In the UK a class or form tends to mean the same thing. A group of young people who study in the same classroom during one school year. In most schools there would be several such forms who, together make up a year. Most UK schools so not use grade in this ...
What does the whole part in bold say?
It's just saying what Harry is imagining.
You could break it down like this:
... for a moment Harry imagined
coming here with Dumbledore,
of what a bond that (=coming here with Dumbledore) would have been,
of how much it (=coming here with Dumbledore) would have meant to him.
So, Harry "and ...
Lemonade is being used as a non-count or mass noun, because the enquiry was about the nature or composition of the drink. What is the black stuff in that pile on the ground? It is coal. What is that white powder on your hands (e.g. to a baker)? It is flour. What are honey gushers? It [a honey gusher] is lemonade.
In this case "out of" means because of, he's saying his lifestyle is the result of a choice. The phrase "out of" has many meanings and you see it used in a lot of different contexts. The link provided lists the various ways "out of" can be used, and includes the because of meaning I mentioned.
"You sure this time?” Langdon didn’t bite.
Olivetti is questioning Langdon's credibility, it sounds like Langdon was wrong about something before... - he is asking if Langdon has made [another] mistake.
Langdon didn’t bite.
Is exactly as you think, it's a sideways reference to him not 'taking the bait', the bait being Olivetti's criticism - Olivetti ...