The ending scene is too heartbreaking, that I have only watched until the end one time.
The final scene is too hard to watch that I have only watched the whole movie once.
The last scene is too painful that I have only watching the movie from start to finish one time.
「最後のシーンが辛すぎて最後まで観れたの1回しかない」は英語に訳すとこのようになります。
The ending scene is too heartbreaking, that I have only watched until the end one time.
The final scene is too hard to watch that I have only watched the whole movie once.
The last scene is too painful that I have only watching the movie from start to finish one time.
最後のシーン→ the last scene/the final scene/the ending scene
辛すぎる訳：
too heartbreaking → 心が辛い
too painful → 辛すぎる／痛すぎる
too hard to watch → 見るのが辛すぎる
（映画を）最後まで観るの訳：
to watch until the end → 終わりまで観る
to watch the whole movie → 全部観る
to watch the movie from start to finish → 始まりから最後まで観る
ご参考までに。
The last scene was so heartbreaking that I’ve only managed to watch it all the way through once.
こんにちは！
ご質問ありがとうございます。
ご質問について、いくつか言い方が考えられますが、例えば、
The last scene was so heartbreaking that I’ve only managed to watch it all the way through once.
とすると、「最後の[シーン](https://eikaiwa.dmm.com/uknow/questions/32096/)が辛すぎて最後まで観れたのは1回しかない。」となります。
役に立ちそうな単語とフレーズ
heartbreaking 辛すぎる、胸が痛む
manage to ～ どうにか～する
watch all the way through 最初から最後まで観る
参考になれば幸いです。
アメリカ合衆国 
日本 
