Manon (إلى الإنكليزية ترجم)

As the vid shows, the song alludes to a famous tragic story. In the novels, the character did horrible things to get his hands on some mountain spring, which eventually led to the death of Manon's father. Manon learned by chance about all this and hates him with all her heart. Tragically, he doesn't suspect that and so will pledge a pathetically unrequited love to her.
The song makes Ugolin look like a kind of peasant-poet. In the books, while he's not a mean character, he's still quite ungainly, uncouth, horribly stingy and not very bright

moi je -> "quant à moi" or "moi, je" are very common in French but they don't translate that well into English. It's just a light emphasis, nothing as strong as "me, I...". For instance the first few lines could be rendered with "she sings while I cry", etc.

j'en meurs -> the "en" means "because of it" (she dances and it kills me)

"j'en crève" is close to "j'en meurs" ("It's killing me / eating at me")

Mais moi je l'aime -> but I love her

Je me coucherai sur toi -> more like "I will lie on you" (meaning he will keep her warm with his body heat). The metaphor is a bit crude.