Alejaste comes from the verb alejarse, meaning "to distance oneself" or "to move away". It's a poignant word that captures the pain of a relationship ending.
In the song, the lyrics
This song is a powerful journey through the pain of a breakup. The singer looks back on the sweet beginnings of a relationship, remembering the "primer beso" (first kiss) and the "primer mes" (first month). But now, she's faced with a heartbreaking contrast: receiving the "último beso" (last kiss) for the very first time. It's a confusing and lonely experience, as she wonders if her ex made her fall in love only to leave her all alone.
The lyrics reveal a deep internal struggle. On the outside, she tries to pretend she's moved on ("por fuera me engaño" - on the outside, I fool myself), but on the inside, she desperately misses him ("por dentro Te extraño" - on the inside, I miss you). He promised forever but then cut things off, leaving her with a love that was given and then suddenly taken away. Even after a year, the pain is still fresh, and she doesn't know how to erase the memory of "you and I."