Answer:
These lines show that her love is all encompassing. It is absolutely stretched to the limits. Even when she feels as though her existence might end, it is the love for her husband Robert that sustains her.
Explanation:
This is one of my favorite poems from the victorian era. Elizabeth Browning lived a sad life until she was 40, but during that time she wrote amazing poetry. This particular poem was unique for a couple of reasons. During the era, it was written most love or heartbreak poems were directed at (him/her), but Liz did not do this. Secondly, she and her husband had eloped and married without her father's permission. She was forced to live with her father and endured his cruel neglect for 2 more years after she was married. This poem was written and sent to her husband during that 2 year period.
I hope I didn't bore you. Good luck with your class,