I'm sorry I didn't wait with you for the next train.
Sorry that I got on the train before you. I was thinking that I could have waited with you for the next train.
ご質問ありがとうございます。
① "I'm sorry I didn't wait with you for the next train."＝「あなたと一緒に次の電車を待たなくてごめんなさい。」
② "Sorry that I got on the train before you."＝「あなたより先に電車に乗ってごめんなさい。」
"I was thinking that I could have waited with you for the next train."＝「あなたと一緒に次の電車を待つことができた、と考えていました。」
ご参考までに。
"先に帰ってごめんね"
- I'm sorry I left first.
- I'm sorry I left without you.
- I'm sorry I went home first.
例：
I'm sorry I left first. I could have waited for the next train with you but I didn't want to get in between you and your (boyfriend/girlfriend/partner).
- 先に帰ってごめんね。一緒に次の電車待ってあげればよかったのに、あなたと（彼女・彼氏・パートナー）の邪魔になりたくなかった。
アメリカ合衆国 
