I have lost my faith in people, so I can't open up to anyone.
誰もを英語では、
'Anyone', 'Nobody', 'Anybody' などといえます。
信じられ名うなったというのは、
'I can't trust anybody anymore'
'I feel like I have lost faith in people'
と言った表現を使って頂ければと思います。
どうぞご参考までに。
本文に書かれた方については、
He can’t trust anybody because he has been treated badly by many people since his childhood. He is scared of people.
「彼は誰も信じることができない。なぜなら幼少期からたくさんの人たちにひどい扱いを受けてきたからだ。人が怖いのだ。」
と訳すことができます。あくまで一例ですが、参考になれば。
He had a difficult upbringing and now finds it hard to trust most people.
He has lost faith in people because of a difficult childhood.
Upbringing' is a word used to describe the time in a child's life when they rely on adults to look after them and 'bring them up' or helping them to become 'good' adults. If someone has a difficult or bad upbringing it can effect them for the rest of their lives in many ways, and trusting other people is one of these knock on effects.
When you lose 'faith' in someone or something is means that you do not believe in it anymore. This is similar to trust.
upbringing'（子どものしつけ）は、子ども時代の親にしつけられる期間を表します。
'upbringing'は、いろいろな形でその人のその後の人生に影響を与えます。人を信じられるかどうかもその一つです。
'to lose faith in someone/something'は「～を信用できなくなる」という意味です。'faith'は'trust'（信頼）に近いです。
"He is untrustworthy" is a formal way to say that a person can no longer be trusted. This person typically was a friend or family member in the past, but has done something that broke that trust. This phrase could be applied to someone who steals, lies or has a tendency to gossip about others behind without them present.
"He is untrustworthy"（彼は信用できない）は「もう信用できない」と表すフォーマルな言い方です。この "he"（彼）は大抵、信頼を裏切るようなことをした元友達や家族です。このフレーズは、人の物を盗んだりうそをついたり陰口を言ったりする人について使うことができます。
He does not trust anyone because of how badly he was treated by many people when he was young
He does not trust people because of how badly he was treated when he was young
When you want to explain that a person was treated badly by others when they were young to the extent that it affects how they are unable to trust others, the you can say it in the following ways:
-He does not trust anyone because of how badly he was treated by many people when he was young
-He does not trust people because of how badly he was treated when he was young
幼い頃にひどい扱いを受けて、人を信用できなくなった人を表す言い方です：
【例文】
-He does not trust anyone because of how badly he was treated by many people when he was young
［訳］彼は幼い頃、多くの人からひどい扱いを受けたので、誰も信用しません
-He does not trust people because of how badly he was treated when he was young
［訳］彼は幼い頃にひどい扱いを受けたので、人を信用しません
If you feel the need to mention the reason for his lack of trust, you can simply add, "due to his past/history".
However, these two examples can be used simply to state that:
1. The person has a lack of trust and will not trust or believe people easily. It will be tough to get him to believe you or to trust in you.
2. "He is ALWAYS skeptical" - the adverb of frequency "always" shows that this is a regular occurrence. Pairing it with the word "Skeptical" shows his lack of trust in things.
その人が人を信用できなくなった理由を伝える必要があるときは、"due to his past/history"（彼の悲しい過去のせいで）を付けることができます。
上記二つの例文は以下の意味で使うことができます：
1. 彼は人を簡単に信じたり信用したりしない。彼に信じてもらうのは大変だろう。
2. "He is ALWAYS skeptical"
［訳］彼はいつも懐疑的です
- 頻度を表す副詞 "always" は、いつも起こる事を表します。"Skeptical"（懐疑的）と組み合わせて、信頼の欠如を表しています。
おっしゃられている内容は以下のようにも表現できると思いました(*^_^*)
He can no longer trust anyone.
「彼はもはや誰も信用できない」
no longerは「もはや～ない」の意味です。
例）
I no longer like it.
「私はもうそれを好きじゃない」
以上です。
少しでも参考になれば幸いです(*^_^*)
★★大阪カフェレッスン英会話講師KOGACHI
He lacks trust in people example sentence: The young boy experienced so much pain and constant disappointment in his past that he lacks trust in people these days.
He is difficult to convince example sentence: Many people close to the you boy lied and abused him so now it is very difficult to convince him that his new family won't hurt him like the previous one did.
Has little faith in people example sentence: The you boy went through a lot of torture and pain from people he thought loved him so now he has little faith in anyone.
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