I know what my heart is like
 Since your love died:
It is like a hollow ledge
Holding a little pool
 Left there by the tide,
 A little tepid pool,
Drying inward from the edge.
This “little pool” may be a puddle of her tears. Or perhaps it is a metaphor for her emotions-the feelings of heartbreak. 
 The water similes used in this poem are powerful. Water is commonly used as a metaphor for Time in poetry-for it to be shrinking and small may symbolize her Time (her life) slowly running out.
Ebb