もしおれとわかれたらおれしぬからな　moshi oreto wakaretara ore shinu kara na

もしわたしとわかれたらわたししぬからね　moshi watashito wakaretara watashi shinu kara ne

(For a more accurate translation, please explain in more details about the sentence you want to say e.g. in what context , in what kind of situation etc)