Does the line before the last read better as
Next year who will come to this place? (maybe)
Just a suggestion to shorten that line.

on a holiday with you
walking the lonely forest path
as we both knock kneed our way passed
slowly first then fast
ere the sun fell half mast
lovely poetry well at last!

You, the subject of the poem, is walking in the end of the fullness of summer into the fall, seeing signs, and alluding to death and aging. The symbolism is immediate. I would perhaps consider developing the horse to be a symbol of death, as he is the the only real figure accompanying you on this nature walk. He is ancient and strong enough to "bolt" and his long "bound" shades you from the sun. Bound here is used as a noun, which I cannot find a proper meaning with. He decides to let you be, but you wonder if he will not be so kind next year. Just a simple word or image could allude to the horse as this symbol...Just a thought to make the action in the poem bigger than itself into a more symbolic universe. I hope my commentary is not too presumptive.

Where I grew up we just referred to deer as all deer, although I have known buck is used in the country...my first take was the horse because that's what we called horses in Queens.
I still feel the animal could be a symbol- nature, youth, regeneration...I think it needs a larger purpose to be in the poem rather than your shared common mortality. Anyway, that was my take...