Not a form I'm familiar with, but it's kind of close to a Shakespearean sonnet. Rhymes and rhythm mostly good, but just a little forced in a couple spots. I'm having a little trouble figuring out the meaning. I think it refers to two people who cared about each other but are now far apart, but I couldn't tell whether they still care for each other or if this is post-breakup. Or maybe one's moved on and the other hasn't. The language in the poem itself seems that way, that the speaker is telling the other person they need to let go, but the title implies the opposite (nice pun there, btw). Maybe it's just that the prompt is a common expression I've never heard before, so I don't know what meaning it inherently carries.

The horse line in particular felt odd, as maybe a way of saying the distance is so vast that a horse couldn't traverse it? That was my read of it, but that's an odd choice of transportation reference, given no other context why that would be the most relevant one. Unless it's referring to ponies and the breakdown of the magic of friendship between the two? I'm kind of reaching for ways to interpret it.

The atmosphere is good, and while I could see some readers feeling like the early stanzas' focus on the technicalities of biological circulation is a tangent that runs too long, I thought it made an effective slow transition between the literal heart and the figurative one, possibly indicating the speaker's reluctance to talk about the latter.