The story aspect of this is wonderfully sad but well written and as i always say it never strayed the emotion at all. I even love the word play you used in the first two lines. Although they don't really match the rest of the poem per se they are nice set ups to start the emotions told.

From the first two lines i imagine a person lying in bed having a restless night and possibly even having bad nightmares about this person. You survived the day but at the cost of your sleep. But the third line could be considered a start of a dream almost.

You dream that you are a tree, a broken tree on the brink of your life and you are falling apart limb by limb (or a possible connection bone by bone, broken bones perhaps). The tide could represent this person's blood stream almost but are trying desperately to not drown and their heart you believe is your shelter.

But it is not to be because it turns out that the love you thought you had (the heart being a life raft or boat or shore) turns out to be something in your imagination or in this case bad dream.