I absolutely love this, right up until the last line. 

For the strong, wonderful language you use throughout the poem, the last line rings hollow and cliched to me.  There's the narrator and there's the nonno, so who is "you"?  Why should we care about "you," about why "you" wasn't saved? 

You hint at it, sure.  There's the damaged nonno, mumbling, on a park bench.  Is "you" a lost nonna, someone he loved?  Is "tu" (of "te quiero") the narrator?  Or is "tu" the "you" of the last line?  If so, why is he singing the "new favorite song" TO the narrator (as opposed to AT the narrator, or TOWARD the narrator)?

Maybe another stanza, powerful like your first, between "THIS much!" and "too much," could help frame this for us a little.  A couple of lines that paint a picture of "you" in our heads, that give us some hint who "you" is, so we can care. 

I agree with Elizabeth -- this poem is wonderful, but the last line is a bit of a cop-out.  You have a great image, very understated and personal, but "not enough to save you" drops that feeling.  The piece is rhythmic and song-like, so you might consider taking out the last line and repeating "not enough."  The point would be clear and more subtle.

I love the imagery in the first stanza.