The translation you have done doesn’t fit the meaning of this text.

1. I’ll try to explain the y. It is used to replace a word, previously used after a preposition.

Here the y is supposed to refer to the existence. BUT I think the author means that, in his quest to search for a meaning to his existence, he lost his innocence. Which means the y refer to the whole sentence, and not only to existence.

For example, “je vais au cinéma…tu y va aussi ?” => I’m going to the cinema.. are you going too ? the y is used to refer to cinema

The other preposition you might want to know about is en. It’s the same, but for direct object.

Example : “j’ai mangé une pomme, j’en veux encore une” => I’ve eaten an apple, I would like another one.The en is used to refer to apple.

2. About the second sentence, I don’t think you understood it right

J’ai fini le coeur sans défense => I ended up with a defenless hearth.

Ask if you don’t understand.

3. I explained you earlier about the “en” ^^

4. Same here, try to guess what the “y” is referring too 😉 désinvolture means offhandedness, if you understand the meaning of it in the sentence.

Let me try to answer your questions 🙂

1. y refers to his search for a meaning to his existence. Yes, it’s an indefinite there, even though it’s not really a place, we use it like this.

2. Yes you’re correct, though I would have said an/my instead of the.

3. En has the meaning of by doing so. The sentence is a metaphore, though I’m not sure I understand it, maybe he can’t feel anything with his lips anymore ?

En is a really difficult word to grasp the meaning of. It’s usually used to avoid repetitions in a sentence. It replaces what we’re talking about.

Tu vois ces pommes ? Je vais en faire de la confiture. | See those apples ? I’m gonna turn them into jam.

Tu te rappelles de son numéro ? Non je ne m’en rappelle plus. | Do you remember his number ? No, I don’t remember it.

Je ne sais rien. Question ? Je n’en sais rien. / I don’t know anything. I don’t know anything about this.

Je ne mange pas. Je n’en mange pas. / I don’t eat. I don’t eat that (thing we’re talking about).

Des lapins ? J’en ai vu plein hier ! / Rabbits ? I saw a lot of them yesterday !

You can add en before almost any verbe.

4. Désinvolture refers to being bolt. Y refers to the thing he stops believing in (the lost paradise in ourselves).
   

   Je crois en Dieu. Je n’y crois pas.

/! This is not the same meaning of en, here it means in.