The correct option is B We've been through many travails, some easy, some more difficult.
From the poem's lines " And age it seems since you I began our
March up hill or down. Sailing smooth o'er Seas that are are rare",the poet is indicating the journey that he and his heart have had together, in good times and bad. Therefore, the sentence that best describes what the poet means is option A) We've been through many travails, some easy, some more difficult. The other sentences are incorrect interpretations of the poet's lines and so are incorrect.