Is You and ain't Are You - Tradução em português

There is a song from Hoobastank called ''The Reason''. However, there's a sentence this song who says: '' And the reason is you''. My Doubt is this one. I can't understand very well why is ''Is You'' and ain't ''Are You''.

PS: say me also if i did a mistake writing these words this way.
This is it!

ATIVE O ENGLISH PLUS Além de aprender sem anúncios, você terá acesso: aos Cursos do English Experts, a respostas verificadas por especialistas (ilimitado) e ao aplicativo Meu Vocabulário. ATUALIZAR AGORA
1 resposta
Studying english through songs can be a lot of fun, but there are things you gotta know about songs:

-Sometimes(most times) they're NOT grammatically right.[Because the most important thing on it is the melody, the rythm, etc]
-The kind of language used on music is (most times) coloquial.

So, It's very common we hear "You is", "Goin' "...etc . When we talk about songs grammar is NOT important.

Note: Some songs have very strange expressions. If you want english to pass a test or something important, don't study english by music.

Hope that helps.
Take care