How does the speaker express his undying love for his beloved in the poem?

The speaker expresses his undying love for his beloved in the following ways: First, he compares her to a beautiful red rose. This in itself does not speak to undying love, but the speaker goes on to make comparisons that illustrate how completely devoted he is to her. He says his love is so deep that it will last until the seas go dry. He also says he will love her until the rocks of the earth melt—until the end of time.
He bids farewell to his love at the end of the poem, but promises he will come back to her, even if he has to travel 10,000 miles to do so.
The speaker uses hyperbole (exaggeration) to reassure his beloved that he will stay true to her despite heading out on a journey. He wants there to be no question in her mind of how much he loves her and how loyal he is.