A great tribute to the loved one.
Poet has an inimitable approach to explaining how he depends on the partner to survive. The refrain "There's just this one thing..." is like a mantra that is powerful and effective on the understanding of the reader. God took her/him away exactly because that is one thing even He couldn't do without.
Imagery-
Imagery is visual and touching from the word "go". The casual way of mentioning the extraordinary bond that linked them is one of the merits of this poem. It is as if there is conversation between them, telling her how much he misses her.
"There's just this one thing I can't say
And that's how badly I'd like to wake up next to you"
Flow-
Flow is unstoppable with powerful feelings and memories expressed in simple word choices.

A poem after my own heart.

Write on!