nemesae-san, I admire your effort. Poem writing is not an easy task, even in your own native language, and you tried it with a foreign language!
I'm not much of a writer, so please excuse my Japanese! There is much room for improvement (especially in terms of connection between lines).
化け物手に抱き締められる→亡霊（ぼうれい）の腕（うで）に抱（いだ）かれ
(化け物 is ghost but closer to a monster.)
囁きを聞きって残響じゃないのわｰ>こだましない囁きが聞こえる
君だけ 君だけ→ＯＫ
不在を悼んだ→君（きみ）を偲ぶ
(I omitted "absence" because the word 偲ぶ already suggests absence (by death or distance.)