I think I reviewed something else of yours, but can't find it in your portfolio. Or perhaps another writer did something in a highly similar style.
Technical stuff first. Of structured poetry such as this, my opinion is that
1) The rhythm should be regular, with emphasis falling on the natural stressed syllable of words
2) Rhymes should be unforced, without odd word-forms
3) The rhyme scheme should be regular
Regarding #1, your rhythm is mostly regular iambic, with lines one and three being tetrameter and lines two and four being trimeter, sometimes ending with a trochee, at least in some verses. The rhythm varies throughout the piece, mostly good but with the occasional exception such as "Creased and dragging were my eyes and cheeks;" which either forces the stress onto the -ing or breaks out of iambic; it might be "So creased and drawn my eyes and cheeks" which is perfect iambic tetrameter. "Drawn"--looking strained from illness, exhaustion, anxiety, or pain--also fits your meaning well. "And ever forward we did ramble" could be smoothed: "As forward we did ramble". "Hoping to calm her anxious nerves" works quite well without the "hoping". As for "In a moment of unexpected courage"--please try again, this is not even close to iambic tetrameter and really grated. But since this is a work in progress, I expect that you will continue to work on this. And again, I'm being picky here -- the occasional extra syllable is not a major flaw.
Regarding #2, you use natural rhymes along with a lot of half-rhymes, though "fields"/"words" and "absurd/return" are not even close. Generally, what you have works well, without too many contortions. So mostly good here.
Regarding #3, you keep a consistent ABCB scheme throughout. Again, good here.
Oh, in stanza 6, shouldn't that be "MY eyes gleamed..."? And mightn't the "field of brambles" be more likely to be a "hedge of brambles". You could ride "along a hedge of brambles" which is a nice image.
Now, on to more important stuff.
First, I love the premise, the unexpected encounter with an older--and unpleasant--self. I'm a bit reminded of Thomas Hardy's "I look into my glass". You've a lot of effective scenes - the lonely ride, the fall of night, the fretful horse, the first glimpse of the elder you. Those stanzas are more firmly done. If you examine your work, you may note that from that point, the rhythm becomes looser, the rhymes less precise. Areas for future work.
Oh, dear, I've spent far more time on this than I had intended. A tribute to how much potential I see in this poem.