Ariana Grande is missing her ex ... and it's making us cry!

The singer posted screen shots of her phone playing two singles off Mac Miller's new album Swimming -- "Ladders" and "Dunno."

But her most significant post since the rapper was found dead in his home due to an apparent overdoes, was an open letter she posted on Instagram. It read: "i adored you from the day i met you when i was nineteen and i always will. i can’t believe you aren’t here anymore. i really can’t wrap my head around it. we talked about this. so many times. i’m so mad, i’m so sad i don’t know what to do. you were my dearest friend. for so long. above anything else. i’m so sorry i couldn’t fix or take your pain away. i really wanted to. the kindest, sweetest soul with demons he never deserved. i hope you’re okay now. rest.”