A person is speaking to someone who has walked out of their life, and the poem is split between two very different pictures. The one who left seems free: they wander the world "with no shadow," hurt people without regret, and become someone new each night. The speaker, by contrast, walks with their head down, followed by a shadow that holds "the darkest of things" no one else could imagine.
The feeling is a mix of hurt, resentment, and determination. The speaker admits to sleepless nights spent rereading old texts and replaying voicemails, and says it makes them depressed. But the poem turns when they lift their head and tell themselves, again and again, that they will be okay. The repeated "I will not let" and "I am strong" sound like a pep talk, as if the speaker is convincing themselves as much as anyone else.
The mood is raw and honest. It's sad, but it ends on stubborn resilience rather than despair.