I love making wallpapers like this, even though this is the second kind...
Anyway, like the wallpapers says, this song is called Life is like a boat, by Rie Fu.
I only picked out to verses. I chose this song because I feel it resembles Zero and Yuki's relationship. I shall right the meaning of each line, this is zero at first;
]Nobody knows that I'm a vampire,
For this reason I always fell empty,
And when I really need someone,
Nobody's comforting me, can someone keep me strong?]
Now when he meets Yuki;
[I want you to know That I'm a vampire,
I never thought I'd like you this way,
And if you need me to follow you along,
I'll give you what I couldn't have till I found you, I'll make you strong.

And that's what I think bonds them. (Cool longest description I wrote...)