The 25 year old star took to Instagram to share a short video with a moving caption.
The short video features an intimate moment with her ex-boyfriend during their relationship together.
'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,’ the singer wrote.
'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.'
Website TMZ claims Miller died of an apparent overdose.
The couple split after two years of dating in early May.
"This is one of my best friends in the whole world and favorite people on the planet, Malcolm McCormick," the 25-year-old singer said at the time of the split. "I respect and adore him endlessly and am grateful to have him in my life in any form, at all times regardless of how our relationship changes or what the universe holds for each of us."