姐姐弟弟走了！弟会永远的记住你的

Dear sister, I'm leaving. But I'll always remember you.
By: Your Younger Brother

Dear my younger brother。I'm going away now .But ill remember you forever.
亲爱的弟弟，现在我离开了，我将会永远想念着你的。

My older sister, I'll/am going to/leave(I've left)/I must be off. I'll/I'm going to/ remember you forever(I'll always remember you). --Your younger brother.

Dear sister, I must be off now, but I will remember you forever.

Dear elder sister, your younger brother who has gone will keep you stay in his mind forever.