Añorarlo comes from the verb añorar, meaning 'to long for' or 'to yearn for'. It's a beautiful and somewhat melancholic word that expresses a deep sense of missing something or someone from the past.
In the song, Camilo sings, "No esperar que se haga recuerdo pa' añorarlo después" (Don't wait for it to become a memory to yearn for it later). He uses this word to convey the regret of not appreciating the present moment, only to miss it intensely once it's gone. It's a poignant reflection on cherishing what you have now.
Camilo spends this whole song annoyed at himself for being somewhere else while his life was happening. He admits it in the first two lines: "Tengo en la mira la trampa" ("I've got the trap in my sights"), and then "E igual me vuelvo a caer" ("and I still fall into it again"). The trap is the future. "Me perdí de lo que hacía" ("I missed out on what I was doing"), he sings, "Pensando en lo que haría después" ("thinking about what I would do later").
Then one line turns it around: "Después de todo, entendí que el tiempo se quedará" ("after all, I understood that time will stay"), "Y seré yo quien se habrá ido" ("and I will be the one who has gone"). The chorus does the arithmetic out loud. "Si hubiera sabido" ("if I had known") "Que era la última vez" ("that it was the last time"), "Tal vez no lo hubiera sido" ("maybe it would not have been"). What keeps this from turning into a lecture is how small the things he misses are. He does not reach for milestones, just morning light on a face, "Y las pequitas de tu cara se alumbraban" ("and the little freckles on your face lit up"), and the end of a day, "Y conmigo te acurrucabas y soñabas" ("and you curled up with me and dreamed").