Here are 12 sad short sentences in English:

1、The raindrops remind me of the tears I cried alone.

2、The memories we shared are now just a distant echo.

3、My heart is broken, and there's no one to mend it.

4、The past is gone, and I am left with only the pain of loss.

5、I wish I could forget you, but you're etched in my memory.

6、The wind whistles through the streets, carrying the sound of your voice away from me.

7、My heart feels empty, like a boat without a destination.

8、The nights are long and lonely without you here by my side.

9、The sadness is deep, and I can't seem to find a way out of this pain.

10、You were the one I thought I would love forever, now all I have left is broken promises and tears.

11、Love lost can't be found, even with a heart that's ready to begin again.

12、Each night brings the haunting realization that the one who brought so much happiness can also leave such empty sadness behind.

Hope you can feel these 12 heartfelt sad short sentences, although remember they're simply written for conveying the deep sentiment; never-end regret is a poor medicine, do yourself well after writing/listening them down from tenses' sad words.