By that time I had lost (all) interest in the idea.

那时我已经对此想法（完全）失去兴趣了。

《牛津词典》

I knew right then that I had lost my best friend.

我那时就知道我失去了我最好的朋友。

youdao

While making the kits, I realized that I had lost sight of the true meaning behind it.

在制作文具包的时候，我意识到我忽略了它背后的真正含义。

youdao

I felt as though I wasn't myself anymore, I felt I had lost everything,".

VOA: standard.2009.12.25

On the South Side of Chicago, I worked with families who had lost jobs and lost hope when the local steel plant closed.

VOA: special.2009.01.12

"I was just in Sri Lanka last week and in Indonesia about a month ago talking to people who had lost family members and the loss,the sorrow, the irreplaceable loved one is still felt.

VOA: standard.2009.12.26

Having been away for so long, I had lost that visceral connection I once felt.

WSJ: Fearlessness and Loving in Cairo | Traveler's Tale

Brian Ashton explained his decision by saying I had lost my spark from the World Cup.

BBC: Andy Gomarsall column

You would have looked at me as if I had lost my mind.

FORBES: Dividend Stocks Pay You Better Than The Government