This poem has the word "husband" in the title, so it's no surprise that the poem is about marriage. "To My Dear and Loving Husband" describes a near perfect union between two people. Both the speaker and her husband love each other very much, and their marriage is so perfect that they are, essentially, one person (marriage is all about union, after all). At the same time, the speaker repeatedly describes her relationship with her husband in terms of payment and recompense, which makes marriage sound kind of like a business arrangement. That's a little odd, right?
While the speaker claims she and her husband are soul mates, the formal language of the poem ("if…then," "if…then," 'if…then") makes marriage and love seem less passionate and more logical than we might at first think.
Marriage is based on a love so deep that two people seem like one. Even the basic language of the poem illustrates this sameness, with the repetition in the first three lines of the poem (the speaker says "if ever" three times).