In the poem "The Last Ride Together" by Robert Browning, what do stanzas 6-8 mean?

Robert Browning's poem “The Last Ride Together” is the monologue of a dejected lover as he contemplates the end of a relationship. The title of the poem comes from the setting in which the poem takes place—on a final ride that the speaker and his ex-lover share. Stanzas six, seven, and eight (lines 56-88) strongly develop the character of the speaker and reveal the speaker's attitudes about the end of his relationship. These three stanzas are explained below. Stanza VI
What hand and brain went ever pair’d?What heart alike conceived and dared?What act proved all its thought had been?What will but felt the fleshly screen?  We ride and I see her bosom heave.        There’s many a crown for who can reach.Ten lines, a statesman’s life in each!The flag stuck on a heap of bones,A soldier’s doing! what atones?They scratch his name on the Abbey-stones.        My riding is better, by their leave.
In the sixth stanza, the speaker becomes philosophical about the end of his relationship, considering the nature of love, reality vs. dream, and the nature of failure. The speaker considers that all men fail. In mentioning statesmen and soldiers in this stanza, the speaker justifies his failure, explaining that all men—even those held in high regard—do fail. 

Stanza VIIWhat does it all mean, poet? Well,Your brains beat into rhythm, you tellWhat we felt only; you express’dYou hold things beautiful the best,          And pace them in rhyme so, side by side.’Tis something, nay ’tis much: but then,Have you yourself what’s best for men?Are you—poor, sick, old ere your time—Nearer one whit your own sublime        Than we who never have turn’d a rhyme?Sing, riding’s a joy! For me, I ride.
In this stanza, the speaker continues his philosophical musings with false optimism. The speaker compares himself to a poet, who has only words, whereas the speaker at least has his final ride. The speaker's long thoughts on the poet (an entire stanza) serve as a distraction from his loss, while at the very end, he consoles himself, saying, "For me, I ride," as he accepts the reality that this is the final ride with his lover.Stanza VIIIAnd you, great sculptor—so, you gaveA score of years to Art, her slave,And that’s your Venus, whence we turn        To yonder girl that fords the burn!  You acquiesce, and shall I repine?What, man of music, you grown grayWith notes and nothing else to say,Is this your sole praise from a friend,       ‘Greatly his opera’s strains intend,Put in music we know how fashions end!’  I gave my youth: but we ride, in fine.
Stanza eight is a continuation of the speaker's justification in the seventh stanza. In the seventh stanza, the speaker compared his relationship to the labors of a poet, and decided he preferred the in-the-flesh experience of love over the intangible beauty of poetry. In the eighth stanza, that line of thought is continued, but this time the speaker compares his ended relationship to the work of sculptors and musicians, which he claims is also intangible. Although the speaker appreciates the labors of both of these artists, he still decides that he prefers the love he had, even though it is at its end. Again, the stanza ends with his decision, "I gave my youth: but we ride, in fine."
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