This is the 13096th most frequent German word.
alleinlassen
To leave alone.
Here, 'alleinlassen' indicates asking someone not to let or leave the speaker alone.
Ich bitte dich, mich nicht allein zu lassen.
I ask you not to leave me alone.
In this sentence, 'alleinlassen' is used to express the action of leaving someone, specifically a child, by themselves.
Sie konnten das Kind nicht so allein lassen.
They couldn't leave the child alone like that.
The verb 'alleinlassen' here depicts the act of leaving someone to deal with their issues on their own.