I think “borne”, in either its “Pierre indiquant une distance” sense or in its “Familier. Kilomètre” sense (from Larousse.fr) could be used to capture the notion of [a measure of] distance perhaps in a less technical (or at least more casual) manner than would “kilomètre,” but as for being more romantic or poetic, I think that would depend more on the words accompanying whatever word you choose for “distance” than on the chosen word itself.
That is to say that I think the following phrases would be just as romantic (or not) whether one uses “kilomètre,” “borne,” or any of the good answers given so far:
“Borne après borne, kilomètre après kilomètre, nos corps s’éloignent,
[mais nos cœurs garderaient à jamais l'empreinte de notre amour.]”
“Malgré toutes ces bornes et tous ces kilomètres qui nous séparent, [nos
cœurs garderaient à jamais l'empreinte de notre amour.]”
“Hélas, 1000 bornes/kilomètres nous séparent, [mais nos cœurs
garderaient à jamais l'empreinte de notre amour.]”
(please note that the final bracketed clause in all three of my examples comes from Gaby Bernier: Tome 2 1927-1940, by Pauline Gil, via Googlebooks, whereas the first clause of my examples, at least to the extent that they are not good and idiomatic French, are essentially of my own doing)