I felt a sense of calm wash over me at the end. The patience and love and understanding of waiting with someone through their darkness. Not just skipping over it, invalidating the hardship of what they go through or walking away, but being there when the depths are dangerously low. When there's little air. Sometimes we cannot do much other than give our support and wait for them until the sun is visible again, until they resurface.
A powerful poem, written with a beauty in seeing the person and acknowledging that they are worth it to stay with through the darkest days. A simple write, but a profound message. I also liked the few words per line. My only suggestions:
In the tenth line: I’’ll should be I'll - apostrophe instead of quotation mark
in the beginning lines, "If you were the" and "I’m not scared" felt a bit awkward tense-wise. Perhaps phrase to "If you're/you are the deep dark..." since it would align with the present tense focus. Or have it read "If you were the.." and "then I wouldn't be scared". If that makes sense.
If anyone ever asks why form is so important in poetry, show them this. Such a simple, evocative poem elongated and stretched with great, perhaps purposeful use of sibilance. There's a romantic calmness in this poem, which is given a boost by how your carefully chosen words leak down the page. Well written :)