She compares herself with a creature because she wants to express that she is a human being with lots of feelings and emotions. Here ‘creature’ is used as opposed to nonliving things. If she were lifeless, she would have remained unchanged with time. But for being a ‘creature’ her thoughts or feelings might change later. So it won’t be wise enough to love her for such transitory reasons.

In another interpretation, the lover does sympathize with the poet and wipe her eyes in times of sorrow. All these are similar to treat her like a creature. But the poet doesn’t wish to be treated that way, as she may find a strong position and may not need to weep in future. She wants to be treated with genuine love and care, not with pity.

She compares herself with a creature because she is miserable with sorrow and weeps in a wretched state.

By comparing herself to the creature she wants to say that she is a thinking woman who deserves the same love and respect as any other human being

The poet alludes herself to a *creature* like a whimpering dog or a baby bird that can easily invoke pity in someone’s heart.  She says so that she is not a creature  and if bores his company she’ll forget her pain and might not cry and might not be able to produce the pity and gain sympathy.  She’ll not be able to shed any tear to be wiped off.