However rare true love may be, it is less so than true friendship.

Romance gets the attention while the rarer thing goes unremarked. Deep friendship has no ceremony, no formal commitment and no outside pressure holding it in place, so it survives only on the continued choice of two people who could easily drift. Nothing obliges anybody to keep it going.

That is an argument for treating your closest friendships with the seriousness usually reserved for a partner. Put the visit in the calendar, say the affectionate thing out loud, notice when someone has gone quiet. Whatever has no structure around it has to be maintained deliberately.