と思ったのに

even though I thought...

→ と
phrase Uncommon #18,884
even though I thought... Expresses disappointment or surprise that reality was different from what was expected. Often translates naturally as “I thought..., but...” The casual form 思ってたのに is also common.
JA: うまくいくと思ったのに、失敗してしまった。
EN: I thought it would go well, but I failed.

あれ喜ぶと思ったのに

Huh, I thought you'd be happy.

もっと早く終わると思ったのに

I thought it would be over sooner.

— Брат 2 (2000)

祥太すごいと思ったのに何やってんだよお前

(Shota) I thought you were amazing, but— (Osamu) What the hell are you doing?

— 万引き家族 (2018)

いまやろうと思ったのに

I was just about to do it.

全て順調だと思ったのに

I thought everything was going smoothly.

誰も気付かないと思ったのに

I thought no one would notice.

— パンズ・ラビリンス (2006)

あれ喜んでくれると思ったのに

Huh, I thought you'd be happy.

ボートを買おうと思ったのに手違いなんだ

I meant to buy a boat, but there was a mix-up.

— アメリカン・ギャングスター (2007)

うまくいったと思ったのに

Just when I thought it had worked out...