to hell and back字面意思到地狱再回来，引申为患难与共。

【例句】
We'd been to hell and back together and we were still good friends.
我们曾经患难与共，现在依然是好友。

Josh and I have been to hell and back growing up, so I knew I had tohave him as my best man at my wedding.
乔希和我曾经患难与共的发小，所以我知道我的婚礼上必须有他作为我的伴郎。