I have a couple comments!

For the (mostly) repeated line "Lourde erreur prendre un cœur / Avant son heure," a basic gloss (word-for-word translation full of all the crunchy bits you like) would be something like: "heavy mistake to.take a heart1 / before it1[poss] hour." Un cœur, a heart, is probably not the subject, but rather the object of prendre, that is 'to take a heart'. The weird part of this line is the lack of a finite verb, implying an artistically omitted 'is'. Thus, a basic translation should probably be something like "It is a heavy mistake, taking a heart / Before its time."

In the line "Il faudra attendre," il, the third person singular masculine subject pronoun (that is, "he") is non-agentive (nor is it the theme or the goal or anything else), but rather acting as a placeholder required by the verb 'falloir' which takes no logical subject. (Think "it's raining." In that context, 'it' doesn't actually mean anything, it just has to be there because the grammatical subject position isn't allowed by the language to be empty.) A direct translation would be something like: "It will be necessary to wait," which in context should probably be changed to "You must wait."

tl;dr (without ling babble)
Lourde erreur prendre un cœur / Avant son heure = Heavy mistake to take a heart / Before its time ~ It's a heavy mistake, taking a heart / Before its time
Il faudra attendre = It will be necessary to wait ~ You must wait