Recomenzar means "to restart" or "to begin again." It is a richer word than the plain "comenzar" (to begin), since the prefix "re" adds the sense of starting over after a pause, a setback, or heartbreak.
In the song, the line "La fuerza que me mueve dentro para recomenzar" ("the force that moves me inside to start again") uses the word to describe the inner strength needed to rebuild a life or a love from scratch.
"Yo Te Amo" is Chayanne's plainest possible love letter. He opens by saying he doesn't need fancy words - simple language is enough to say he misses someone and that they are his whole world.
The song is really about total, unguarded devotion. He promises to grow through love rather than fear losing it, and pictures himself as a shelter: "look at my chest, I leave it open, so that you live in it."
By the end he drops any hesitation completely, singing "I belong to you, all of me." It's a song about choosing someone fully, without holding anything back.