その時一緒にいなくてよかったねって英語でなんて言うの？

～でよかったね＝It's good that... 一緒にいなくてよかったね＝you were not with... 主語が「私と」であれば、 It's good that you were not with me 主語が「彼と／彼女と」であれば、 It's good that you were not with him/her 主語が「彼らと」であれば、 It's good that you were not with them あの時＝at that time 是非参考にしてみてください。