I wasn’t able to ask you because I got sad at the possibility you wouldn’t tell me.
I had been curious for a while, but I wasn’t able to ask you because I got sad at the possibility you wouldn’t tell me even if I asked you.
ご質問ありがとうございます。
「もし教えてもらえなかったら悲しいから聞けなかった」は英訳すれば、「I wasn’t able to ask you because I got sad at the possibility you wouldn’t tell me. 」になります。
このような情報が足りないので、「ずっと気になってたんだけど、聞いてもし教えてもらえなかったら悲しいから聞けなかった」にも英訳しましょう。
「I had been curious for a while, but I wasn’t able to ask you because I got sad at the possibility you wouldn’t tell me even if I asked you. 」
ご参考になれば幸いです。